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Microbiology
- the study of microorganisms (microbes)
- viruses, bacteria, parasites, fungi, & others
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Prokaryotes differ from eukaryotic cells in that...
they do not have membrane bound nucleus, membrane bound organelles, or DNA that is organized into chromosomes
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Prokaryotic Cell structures
- Cytoplasm, ribosomes, nucleoid (chromosome), inclusion bodies,
- SOME have capsules and some have plasmids
- *SINGLE-CELLED ORGANISMS
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kingdom Monera
- consists of all the single-celled prokaryons
- consist of bacteria and cyanobacteria (blue green algae)
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How are all living cells divided?
- Into 5 kingdoms, and are classified as either prokaryotes or eukaryotes
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5 Kingdoms of living things
- Plantae, Animalia, Protista, Fungi, Monera
- "Pleasantly Ask Properly For Money"
- Kingdoms Monera, Protista, and Fungi especially cause problems for humans
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What kingdom do the prokaryotes belong to, what does it consist of?
- Prokaryotes belong to the Kingdom Monera and consist of the bacteria and cyanobacteria (blue-green algae)
- *all bacteria and other prokaryotic organisms are earth's most abundant form of life, inhabiting nearly every environmental niche on the planet and are among the smallest organism.
- *despite small size, bacteria have maximum surface area for absorption of nutrients.
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nucleoid
- a nuclear region in prokaryotes which is the cell's single chromosome
- circular structure consisting mostly of DNA with small amounts of RNA
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-oid
medical terminology ~ resembling something
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inclusion bodies
store molecules essential to cell function
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Ribosomes in prokaryotes
- consist of RNA and protein
- are abundant in cytoplasm of bacteria, often grouped in long chains called polyribosomes
Like in eukaryotic, made of large and small subunit and serve as site for protein synthesis
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cytoplasm in prokaryotic cells
- fills cell, consisting primarily of water and substances either suspended or dissolved in the water.
- These substances include lipoproteins, carbs, lipids and various enzymes.
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plasmids
- self-replicating extrachromosomal DNA that carry one or more pieces of genetic info
- One way bacteria can exchange info.. (Ex: becoming antibiotic resistant)
- not required to sustain life
- In pic, kinda oval, spherical loopy shape
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capsule
- some prokaryotes have ability to secrete a capsule
- a protective structure that serves as a defense mechanism.
- tightly bound to cell wall, forms a gel-like (slime) covering that surrounds the bacterial wall
- Human phagocytes (cells that eat foreign invaders) have difficult time attacking
- capsule is considered a major contributor to pathogenicity
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prokaryotic cell walls
- main function is to provide (maintain) shape and stability
- long polymer resembling a chain-link fence
- on top of cell membrane
- contain large polymer called peptidoglycan
- many antibiotics target the cell wall
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peptidoglycan
- makes up prokaryotic cell wall
- an immense, covalently-linked molecule arranged in layers resembling multiple layers of a chain-link fence which gives the cell support
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cell membrane of prokaryotic cell
- also called plasma membrane, DEEP TO CELL WALL.
- Think of it was the "wall paper"
- just like in eukaryotic cell is bi-layer
- regulates transport of material in and out of the cell by transport mechanisms
- contains many complex molecules, including phospholipids, long-chain fatty acids and proteins
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flagella
- used for locomotion
- organisms displaying a flagella are capable of various degrees of movement, and are said to be motile
- About 1/2 of all known bacteria have one
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Pili
- singular: pilus, fimbria
- tiny tube-like projections from the cells surface associated w adherence or attachment to other bacteria cells (to transfer genetic material)
- *SEX FOR BACTERIA
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fimbria
another word for Pili
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Shape and arrangement of prokaryotic bacterial cells
- bacteria are characterized by shape and size
- *before specific culture info is available, physicians use location and appearance characteristics to begin antibiotic therapy
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3 major shapes or morphological types of bacteria
- 1st: cocci
- 2nd: bacilli = coccobacilli - vibrios
- 3rd: spirillia and spirochetes
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Cocci/Coccus
- singular: coccus
- ("berry, grain") spherical bacterial cells, non-motile
- subcategories: diplo (pair), strepto (chain), staphylo (irregular cluster) and tetra (group of four)
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bacilli
- Singular: bacillus
- rod-shaped bacteria, ("little rod, wand")
- Included coccobacilli and vibrios
- Ex: e coli
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coccobacilli
- those bacteria shaped btwn a cocci and bacilli
- are oval shaped
- Coccus ("berry, grain") + bacillus ("little rod, wand") = coccobacillus
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vibrios
- the bacteria shaped btwn cocci and bacilli
- exhibit a comma-shape
- *their single flagellum makes them appear to vibrate under the microscope, hence the name
- Ex: Causes cholera
- "collars and vibraters"
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spirilla
- Singular: spirillium
- either loosely-coiled or wavy
- division of one of "third" main bacterial shapes, are long, thin, spiral, rigid rod-shaped cells
- "Will-ya spill em, hold tight!"
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spirochetes
- division of one of "third" main bacterial shapes
- are tightly coiled, corkscrew-shaped rods, non-rigid
- hard to see
- Ex: syphilis
- "phyllis cheats (chetes), uncork the wine n unwind"
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diplococci
cocci found in pairs
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streptococci
- cocci which form chains
- strepto- = chains of
- -cocci = round bacteria
- "Steps have straight lines, like chains are straight lines"
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staphylococci
- cocci which form grape-like clusters
- staphylo- = clusters of
- -cocci = round
- "like when you bang a staph on the ground, round circles in irregular patters..."
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MERSA
Methasone Resistant Staph Aureus
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Divisions of Bacterial Classifications
- Archaeobacteria
- Gram-positive bacteria
- Mycoplasma
- Cyanobacteria
- Spirochetes
- Gram-negative bacteria
- Rickettsias (in eukaryotic cell)
- " Grampa Milo Aready Spoke, Gramndma Can Ride"
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Methods for ID'ing bacteria
- Gram stains
- growth on special agars
- chemical ID helps differentiate and ID
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The Gram Stain
- microscopic method for visualizing bacterial cells
- used when we want a quick look at what organisms might be causing the pt's disease
- Groups medically important bacteria into two categories: Gram positive or gram negative bacteria
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Steps in Gram stain:
- 1 ~ a sample is smeared on slide and fixed w heat
- 2 ~ slide is stained w crystal violet (purplish dye) for 1 - 2 minutes
- 3 ~ Gram's iodine is used to "fix" the crystal violet (helps to retain the stain)
- 4 ~ Acetone is used to decolorize the slide
- 5 ~ counter stain the slide with safranin (pink)
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Gram-positive bacteria
- stain purple
- have thick, peptidoglycan-rich cell wall that also contains teichoic acid, causes retention (holding it in) of crystal violet (blue) dye
- *when it's decolorized and counterstained, it stains purple cause it doesn't let go of the first stain
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Gram-negative bacteria
- stain pink
- have a thin peptidoglycan cell wall and a lipoprotein-rich (again, bi-layer membrane) cell membrane
- releases crystal violet dye when rinsed w alcohol
- The safranin (pink) counterstain is retained
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Why can the lipopolysaccharide in the outer membrane of Gram-negative bacteria be dangerous to humans?
- Gram-neg walls have an outer membrane, contains lipopolysaccharide, which is an endotoxin.
- This is a toxic component
- Endotoxin has been known to kill people with severe infections
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culture media (medium)
- a nutritive substance, such as an agar gel or liquid medium, in which cultures of bacteria, fungi, animal cells, or plant cells are grown
- Can be liquid or semi-solid (called agar, which is kinda jello-like)
- *"agar plate" is the little slides for microscope
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Commonly used agar
- sheeps blood agar (SBA)
- *blood to bacteria is like candy
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in vitro methods of ID and growth of bacteria
- methods in which most bacteria can be studied
- promotes growth of the bacterial cell on artificial culture media.
- can be either liquid or semi-solid forms which contain agar (a neutral, gel-like substance derived from seaweed)
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colonies
- dense masses of bacteria
- how they grow/form when mixed w nutrients
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Different types of culture media
Enriched, Selective, Differential
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Enriched media
- contains substances that bacteria love that encourage the growth of bacteris
- used as general overview of what's growing
- include sheep's blood agar and chocolate agar
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selective media
- contains inhibitors that allow certain types of bacteria to grow and form colonies while inhibiting others
- Ex: MacConkey agar allow only growth of gram negative organisms
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differential media
- roughly groups bacteria based on fermentation of carbs.
- Gram-neg bacteria that use lactose will grow
- grow pink or red, if they don't use lactose, will be clear
- Ex: MacConkey agar which contain sugar lactose. Bacteria that ferment lactose turn red, those who don't are colorless
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MacConkey agar
- pink, has bio-salts n stuff that gram-positive don't like, Gram-neg will grow
- both selective and differential
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Special atmospheric conditions for some bacterial growth
Aerobes, Anaerobic and Microaerophils
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Aerobes
- LOVES OXYGEN
- require atmospheric oxygen, often enhances with additional carbon dioxide (CO2)
- Use special incubators
- Ex: Streptococcus, Staphylococcus, and E. coli
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Anaerobic environment
- require special conditions that remove atmospheric oxygen (O2)
- HATE OXYGEN
- Special chambers and jars that remove atmospheric oxygen may be used ; can use candle
- Ex: Clostridium species which cause disorders such as gangrene, botulism, and tetanus (stepping on rusty nail)
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Microaerophilic
- these organisms grow best in environment of reduced oxygen and increased CO2 (carbon dioxide)
- may be grown in a jar which a candle is lit before jar is sealed. (burning of candle uses the oxygen in jar and adds carbon dioxide)
- Ex: Camplybacter which causes intestinal disorders
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binary fission
- term used to describe cell division in bacteria
- process of growth and division continues as long as favorable environmental and adequate nutritional conditions exist
- also known as transverse fission
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transverse fission
- Term used to describe cell division in bacteria
- another name for binary fission
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Bacterial cell division
- do not have cell cycle
- are continuously dividing and replicating their DNA, as long as their are in favorable and nutritional conditions
- Phases: Lag Phase and Log Phase
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Steps in bacterial cell division
- 1. Nucleoid elongates
- 2. Nucleoid divides, cell wall and membrane begin to form transverse septum (similar to cleavage furrow)
- 3. Transverse septum becomes complete
- 4. Daughter cells separate
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Phases of Cell Division
- Lag Phase
- Log Phase
- Stationary phase
- Decline (death) phase
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Lag Phase
- The "gear-up" phase
- not greatly increasing in #, but metabolically active (growing, synthesizing enzymes, and producing large amounts of ATP)
- do not reproduce in significant #'s during this phase
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Log Phase
- the period of rapid, exponential growth
- generation time: genetically determined period of logarithmic growth
- will continue as long as there are sufficient nutrients and environment has suitable conditions for synthesis of ATP
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generation time
- how long it takes a bacteria to divide
- the genetically determined period of logarithmic growth which varies by bacterial species from minutes to hours
- Most are under 10 hrs
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Stationary phase
- "leveling off" period, the phase of bacterial growth in which non-replicating cells (those dying off) are about the same in #'s as those still reproducing new cells
- Cells are running out of nutrients
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Decline (Death) phase
- happens once the essential atmospheric, temp and nutritional conditions for log phase are depleted
- The # of cells dying is greater than # of new cells arising from division
- cells lose their ability to maintain metabolic funtions
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Symbiosis
- means "living together"
- bacteria may form 3 different symbiotic relationships w a living host:
- Mutalism, parasitism, and commensalism
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Mutalism
- type of symbiotic relationship, both members of association benefit
- Ex: Escherichia coli (E. coli) in large intestine of humans. We provide nice, warm environment; we benefit from Vit. K produced from E. coli, which is essential for clotting process. Also ward off disease-causing organisms and help digest cell walls of plants. So, beneficial.
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Parasitism
- one organism, the parasite, benefits from the relationship and the other organism, the host, is harmed.
- Many types
- Ex: malaria and tapeworms
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Commensalism
- one organisms benefits and the other neither benefits or is harmed.
- Ex: bacteria which live on our skin
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commensals
- the vast majority of microbes that make up our indigenous flora
- living within humans w/o causing disease
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Rubella
- Measles virus
- can penetrate the placenta and infect the fetus
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Herpes virus
- HIV
- another organism which can penetrate the placenta and infect the fetus
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Normal flora in infants & possible infection through the birthing process
- *because they develop in sterile environment, newborns must acquire microorganisms from interaction w their environments ~ over time become part of their human microflora
- Therefore, newborns may become infected w pathogens during birth
- Ex: thrush (yeast) in throat or tongue, on "boonie"
- Group B streptococcus ~ acquired during birth (can be in vaginal tract), can cause severe, life-threatening infection
- Candida (yeast) ~ thrive cause of infant's moist skin and lack of normal flora
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Normal Flora
- a bacteria which live on or in body but do not usually cause disease
- exist either as resident or transient, using secretions of host as nutritional sources
- Most in lower digestive tract
- Always present in varying pop. in following areas:
- The skin and hair (staphylococci, Bacillus species, others)
- Conjunctive (usually match those found of skin)
- Mouth, nose, and throat (staphylococci, streptococci, yeasts... etc)
- Passageways of intestinal, reprod and intestinal tracts.
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Advantage of Normal Flora
- helps prevent disease-causing organisms from getting in and taking hold (causing illness)
- -In skin, conjunctiva, mouth, nose, throat, urinary, reproductive, and GI tracts
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Transient microflora
- "come and go" organisms that exist in same areas occupied by resident flora
- can be acquired almost anywhere, and may persist for hours, months, or years
- may become opportunists
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opportunists
transient microflora which may cause opportunistic infections in hosts whose protective mechanisms have been compromised or the pop. of resident microorganisms change
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concept of probiotics
- when you take antibiotics, your killing off good flora also.
- So, the probiotic is a pill full of normal microbes to help replace the good flora that's being killed off by antibiotic
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pathogen
an organism which benefits from it's relationship with the host, but harms the host - causing infection
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pathogenicity
- often results in disease in the host
- depends on the organism's ability to invade the host, multiply, and avoid damage from host's defenses
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virulence
- term used to describe the intensity of bacterial and other microbial infections
- varies greatly among different organisms, but is always a factor in infections
- Specific pathogenic mechanisms which contribute to this are adherence, colonization and formation of a capsule
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Pathogenic Mechanisms of bacteria
Adherence, colonization, and formation of a capsule
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adherence
- a specific pathogenic mechanisms in which bacteria use the pili to cling to the surface of host cells, multiply and form colonies
- *Ex: staphylococcus aureus has surface proteins that bind to human connective tissues, including blood. Contribute to virulence of S. aureus
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"clumping factor"
- an enzyme which contributes to the virulence of S.aureus
- surface proteins that bind to human connective tissues, including blood
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colonization
- a specific pathogenic mechanism
- once in place within host tissue, bacterial replication forms colonies, and may overcome host defenses
- *colonization by small #'s of non-invasive organisms is normal in all animals including humans
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formation of a capsule
- a specific pathogenic mechanism
- in certain pathogens, the capsule contributes to the organism's virulence because this thick, polysaccharide structure helps organisms resist host defense processes
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invasiveness
the ability of organisms to penetrate host tissue, usually via special enzymes
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examples of enzymes contributing to invasiveness and pathogenicity
- Hyaluronidase
- Coagulase
- Streptokinase and staphylokinase
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hyaluronidase
- an enzyme which contributes to invasiveness and pathogenicity
- also known as spreading factor
- is produced by streptococci, staphylococci & some other pathogens
- the enzyme attacks hyaluronic acid which is the interstitial cement ("ground substance") of connective tissue
- "always think of mayonnaise when you see this, so think of "spreading mayonnaise" - for spreading factor"
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coagulase
- an enzyme which contributes to invasiveness and pathogenicity
- forms blood clots
- produced by some bacteria that accelerates the clotting of blood, often providing protection from host defenses leading to abscess formation.
- species of staphylococcus produce this enzyme
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collagenase
- an enzyme which contributes to invasiveness and pathogenictiy
- breaks down collagen, the framework of muscles
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streptokinase
- an enzyme contributing to invasiveness and pathogenicity
- produced by pathogenic streptococci
- "Kinase" enzymes digest fibrin and prevent the clotting of blood (by digesting blood clots)
- resulting reduction of fibrin allows more rapid diffusion of the infectious bacteria into host tissue
- *Used in human medicine, similar to enzyme derived from streptococcus, for people who form clots in blood when they shouldn't
- Ex: "flesh eating bacteria" is a streptococcus strain that produces streptokinase
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staphylokinase
- an enzyme contributing to invasiveness and pathogenicity
- produced by pathogenic staphylococci
- "Kinase" enzymes digest fibrin and prevent clotting of blood. (digest blood clots)
- resulting reduction of fibrin allows a more rapid diffusion of the infectious bacteria into host tissue
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fibrin
the protein in our blood clots
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toxins produced by bacteria
Exotoxins and endotoxins
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Exotoxins
- very powerful toxins secreted by living bacterial cell
- Mostly from gram-positive organisms
*Botox: exotoxins from botulism, given in very small doses to relax muscles of face, therefore ridding of wrinkles - Ex: botulism, gas gangrene, tetanus, and staphylococcal food poisoning
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endotoxins
- found primarily in gram negative bacteria, are released only when gram-neg organism dies
- particular risk when giving antibiotics which may result in death of many organisms, leading to anaphylactic shock in pt.
- also cause non-specific gastrointestinal symptoms such as diarrhea, cramping, and generalized malaise
- associated w cholera, some types of salmonella & other similar types of toxin-associated bacterial food or water-borne infections
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malaise
- is a feeling of general discomfort or uneasiness, of being "out of sorts", often the first indication of an infection or other disease.
- "general feeling of being unwell"
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endospores
- dormant stage of some bacteria
- form when nutritional and environmental conditions are unfavorable for growth
- have thickened cell walls to withstand harsh conditions such as excessive cold, heat or dryness
- revert to active cells under favorable conditions
- *comprised of core (middle), cortex and spore coat
- Ex: clostridia species that cause tetanus, botulism and gas gangrene
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germination
a process by which endospores, which have been dormant, become active again
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How do bacteria undergo "genetic recombination"
- by three fundamental processes:
- Transduction, transformation, and conjugation
- this exchange of genetic material may contribute to the ability of some bacteria to acquire antibiotic resistance
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bacteriophages
- just "phage" for short
- virus that infects bacteria
- "bacteria-eating"
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prophage
- a piece of bacterial chromosome which has been infected w a virus
- host cell chromosome acquired both phage DNA and genes from previous host
- *virus gets in and takes over host DNA
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Transduction
- an asexual genetic process
- uses a bacteriophage to insert the resistant DNA into the bacterium
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Steps in transduction
- virus invades bacteria, prophage formed in bacterial chromosome
- prophage splits off from bacterial chromosome (leaving some corrupted DNA behind)
- phage DNA incorporating some bacterial genes, replicates
- bacterial cell is lysed (explodes), phages are released
- phage infects new host cell, incorporates into chromosome & new host (again) acquires both phage DNA and genes from previous host
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transformation
- when a bacterium dies, fragments of it's DNA are taken up by neighboring bacteria
- *not all bacteria have the ability to take in pieces and parts from other bacteria
- These naked DNA fragments are taken up by the recipient cell through the action of carrier proteins found in cell membrane
- Fragments are then "spliced" into host cell's DNA by enzymatic action
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Conjugation
- differs from transformation and transduction cause it requires contact btwn 2 bacteria
- utilizes a plasmid
- transfers a greater amount of DNA than transformation or transduction
- *at the F-pilus (sex pilus) that DNA is transferred from 1 cell to another, usually in much larger amounts that other two
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F-pilus
- "F" refers to "fertility"
- sex pilus of bacteria used in conjugation
- allows bacteria to adhere to each other
- "string" or "tube" like "penis" (but not really) from donor bacterium to recipient bacterium, to transfer large amounts of DNA
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plasmids
- extrachromosomal pieces of DNA in cytoplasm of some bacteria (separate chromosomal piece in cytoplasm, besides nucleoid)
- through plasmids, bacteria often develop drug resistance
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resistance transfer factors
plasmids which assist bacteria in developing drug resistance
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genetic recombination leads to
The transfers of DNA which develops new strains of bacterium including antibiotic resistant strains
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antimicrobial agents
- include substances used to specifically treat infectious microbial diseases
- Can be bacteriocidal or bacteriostatic
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bacteriocidal drug
an antimicrobial agent which kills the organism
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bacteriostatic drug
an antimicrobial agent which inhibits organism growth and allows immune defenses to act against the invader
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antibiotics
antimicrobial agents containing substances derived from other organisms
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ways antimicrobials & antibiotics are effective:
- some affect the cell wall (penicillin)
- some disrupt the cell membrane
- some alter protein synthesis and genetic activity
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Spectrum of Activity
- Antimicrobials can either be:
- broad spectrum or narrow spectrum drugs
- spectrum of activity of antibiotics varies among the types of antibiotics
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broad spectrum antimicrobials
are effective against a wide range of microorganisms including both gram positive & gram negative bacteria
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narrow spectrum antibiotics
- are effective against a limited number of microorganisms or a single taxonomic group
- Ex: the use of penicillin to treat streptococcal pharyngitis
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Resistance of Microorganisms to Antibiotics
- increases each year, occurs through:
- Overuse of antibiotics (also through not finishing antibiotics... gives bacteria change to become resistant)
- Plasmids
- Genetic transfer mechanisms
- Development of neutralizing enzymes (neutralize effect of antibiotic)
- Alteration of pathways used by antibiotic
- Altering cell membrane (to block antibiotic entry into bacterial cell)
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Agar Disc Diffusion
- also called the Kirby-Bauer method
- first widely used lab method in determining the susceptibility or resistance of a clinical isolate
- uses paper discs impregnated w a specific concentration of antimicrobial to be tested
- test organism is "seeded" over the plate & incubated for several hours
- Zones of inhibition are measured & compared to those for control organisms w known zone sizes.
- Results are reported as sensitive, intermediate or resistant
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Commonly known bacterial infections in the upper respiratory tract
- Pharyngitis (streptococcus pyogenes), causes strep throat, common in winter
- Other bacterial infections invade ears, eyes, sinuses and upper bronchioles
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Commonly known bacterial infections in lower respiratory tract
- bacteria-caused pneumonia or bronchitis.. organism is down in lungs
- Haemophilus influenzae, Klebsiella pneumoniae, and Streptococcus pneumoniae are top 3 and ALL CONTAIN A CAPSULE VIRULENCE FACTOR
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commonly known bacterial infections in gastrointestinal tract
- often acquired from contaminated food or water
- include Salmonella and Shigella species as well as Staphylococcus aureus
- *E. Coli O157:H7, specific type of E. Coli common to the intestinal tract of cattle, has been linked to contaminated meats and veggies
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Commonly known bacterial infections in nervous system
- involve infections of the cerebrospinal fluid and meninges, can be caused by several bacteria
- Common examples are:
- In young children: Haemophilus influenzae
- In young adults: Neisseria meningitidis
- Vaccines are now available for protection
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Toxin-Induced infections
- caused by organisms who can secrete toxins which either cause disease directly, or trigger an abnormal response in the body which causes illness
- Ex: botulism, tetanus, and toxic shock syndrome
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Two classes of bacteria which must be intracellular to survive
Chlamydia and Rickettsias
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Oddball prokaryotes
- Mycoplasma, Chlamydia, Rickettsias
- don't stain easily, different
- obligate intracellular organisms
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obligate intracellular organisms
cannot live freely, must live inside a eukaryotic host cell
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Chlamydia
- Obligate intracellular organisms
- The most common STD in the US; causing pelvic inflammatory disease (PTD) in women & urethritis in men.
- Another variant causes epidemic conjunctivitis in newborns acquired during passage through the birth canal
- Require a eukaryotic cell for replication
- Ex: Chlamydia trachomatis causes a variety of human infections
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Chlamydia trachomatis
- A complex organism that has multiple serological variants which cause a variety of human infections.
- Ex: Trachoma, STD's and conjunctivitis in newborns acquired during birthing process
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Trachoma
- an eye infection caused by Chlamydia trachomatis
One of the leading causes of blindness in the world
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Rickettsia
- obligate intracellular parasites with complex life cycle
- normally inhabit arthropod vectors (such as ticks, lice, fleas, etc.)
- Transmission to humans is through a bit
- most prevalent in US is Rocky Mtn. Spotted Fever
- Lime Disease
- *Utah doesn't have tick that causes these diseases
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Mycoplasmas
- the tiniest free-living organisms
- unique in the bacterial world cause they do not have a cell wall ~ therefore have no set shape
- diverse in nature, especially in many animal & bird species
- Some species actually make up normal respiratory and urogenital microflora of humans
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Mycoplasma pneumoniae
attaches to surface epithelial cell sites and causes a respiratory disease primary atypical pneumonia (walking pneumonia)
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General nature of viruses
- are obligate intracellular parasites
- need a host cell; virus provides the RNA or DNA to replicate, takes over genetic machinery of host cell
- Contain RNA or DNA (NOT BOTH)
- RNA viruses also contain code for reverse transcriptase, enzyme which makes DNA from RNA
- Are DNA viruses OR RNA viruses
- Over half of all human infectious processes are due to viruses
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Why is it hard to target viruses?
they change their antigens frequently, so they are continually changing
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Viral classification
in general, viruses are broadly classified as either RNA or DNA viruses based on the make-up of their genome
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Viral structure
- Nucleic acid (RNA or DNA)
- Capsid
- envelope
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Nucleic acid of virus
- A virus contains either a single or double strand of DNA or RNA
- in nuclear region
- differing among viral groups
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Capsid (viral structure)
- protective coating enveloping the nucleic acid in viral cell
- determines the shape of the virus
- Composed of capsomeres
- can be helical, polyhedral (multi-sided), or in some cases bullet-shaped
- (NOT TO BE CONFUSED WITH THE BACTERIAL CAPSULE)
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capsomeres
the individual protein subunits which make up capsids
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nucleocapsid
- the combined capsid/nucleic acid arrangement
- (viral structure)
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Viral envelope
- when present, are external to the capsid & are acquired from the combo's of proteins, lipids and carbs found in host cell
- many viruses have glycoprotein spikes
- These structures account for high degree of both host, and host cell, specificity of viruses
- many also serve to "hide" virus from being attacked by host's immune system
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Viral replication process
- also referred to viral progeny
- 5 step replication cycle:
- ~1 Adsorption
- ~2 Penetration
- ~3 Synthesis
- ~4 Maturation
- ~5 Release
- "A Penis Soothes My Rages"
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virion
a single, complete virus unit
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Adsorption
- Step 1 in 5-step viral replication cycle
- Attachment of the virus to host cell
- W/ enveloped viruses, the glycoprotein spikes attach to specific matching sites on hosts cell wall
- W/ naked (non-enveloped) viruses, attach to specific molecular sites on cell surface
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Penetration
- Step 2 in 5-step viral replication
- follows quickly after adsorption, process by which virus enters host cell via endocytosis or fusion w cell membrane of host
- Once inside, virus uncoats
- free strand of nucleic acid then moves to host cell's nucleus
- "Sexual penetration requires no clothes"
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uncoating of virus
upon entering host cell, virus immediately loses envelope and capsid
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Synthesis
- Step 3 in 5-step viral replication
- produces new genetic material and varies btwn RNA and DNA viruses
- W/ DNA viruses, the DNA is synthesized in orderly manner in nucleus, using viral enzymes in transcription
- Proteins are synthesized in cytoplasm using host cytoplasmic enzymes and by using the host cell ribosomes and Golgi organelles
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Maturation
- Step 4 in 5-step viral replication
- the assembly, or "packaging" of the newly synthesized molecules into complete virions (new little baby viruses)
- occurs as soon as abundance of viral nucleic acid, enzymes and proteins have been synthesized
- some viruses are capable of inserting viral genetic material into host's genome permanently, which is then capable of producing new viruses. Can occur years after infection
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Release
- Step 5 in 5-step viral replication
- the departure of the new virions from the host cell
- is this final cycle of viral reproduction that may be the cause of symptoms in host
- Some viruses rupture host cell releasing virions; others release viruses and host cell remains intact in process called budding
- enveloped viruses form their envelopes from host cell membrane as they exit the cell
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Viral Pathogenicity
- viruses are very specific about which animal/animal cell they target for infection
- nature of infection depends on type of virus, system affected and host response
- Several types of viral infections that fall into two main categories: acute and latent (persistent)
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Acute viral infections
- Disease cycle is relatively short
- Host cell rupture and virus spreads to neighboring cells
- After sufficient cellular damage, symptoms rapidly appear in infected host.
- It's up to host's immune defenses to eradicate viral invaders, as well as provide measure of protection from future exposure to viral agent
- Ex: common cold (rhinovirus), influenza (types A and B), hepatitis viruses
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Latent/persistent viral infections
- vary widely in scope
- once in cell, infection proceeds by replication of essential enzymes and proteins, but viral material (also called provirus) remains in host and replicates new virions when "triggered"
- virus becomes relatively inactive but reemerges
- provirus remains in host cell
- Replicates new virions when triggered by some external event (stress, fever, etc.)
- Ex: herpes virus, Epstein-barr Virus, HIV
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herpes viruses
- classic example of virus causing both acute and latent/persistent viral infection
- Cold sores are acute phase of herpes infection
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Epstein-Barr virus
- infectious mononucleosis
- immune system viruse
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oncogenic viruses
- cancer-producing viruses
- possess oncogenes that cause uncontrolled and abnormal division of host cells by altering cell cycle "checkpoints"
- Ex: hepatitis B, Hepatitis C, Human Papilloma virus
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oncogenes
cancer-causing genes which cause the uncontrolled and abnormal division of host cells
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human papillomavirus
virus which has been directly linked to cervical cancer in women
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treatment of viral infections
- MOST EFFECTIVE means of preventing many viral diseases is through use of vaccines
- very few effective therapies; antibiotics are ineffective since they act on bacterial cell components not found in viruses
- Some antiviral drugs do slow down attachment of virus to host cell
- Some simply suppress, do not cure, viral infection
- Vaccines targets at viruses include polio vaccine, Gardasil for cervical cancer, and the hepatitis vaccines
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Prions
- infectious proteins w/o genetic material (meaning no nucleic acid) that come into contact w normal proteins and transform them into more infectious prions
- Prion diseases are found in humans & other animals, derive name from proteinaceous infectious particle
- All known prion diseases affect the cells of the brain
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transmissible spongiform encephalopathies
- the current collective terminology for prion diseases
- "spongiform" comes from cytopathic effect on brain tissue
- infection produces microscopic holes in brain which resemble holes in sponge
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Prion characteristics:
- generally resistant to inactivation by heating to 90°, a temp that will inactivate most viruses
- infection is resistant to radiation treatments which inactivate organisms w genomes
- not susceptible to enzymes that inactivate RNA and DNA
- susceptible to protein denaturing agents
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Examples of Prion diseases
- bovine spongiform encephalopathy (BSE) : "mad cow disease," causes a slow loss of neural function and eventual death. Humans are believed to acquire by ingesting infected animal by-products
- Creutzfeldt-Jakob disease the human variation; slow, neural degenerative disease, resulting in eventual death
- Scrapie variation in sheep
- Chronic wasting disease variation in deer and elk
- NO EFFECTIVE TREATMENT FOR ANY PRION DISEASES
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the kingdom of Fungi
- important for decomposition and recycling of organic material
- include mushrooms
- medically important
- divided into two groups: yeasts and molds
- some are human pathogens, some are toxic and hallucinogenic
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Mold
- produces spores whose arrangement and appearance depend on fungal species
- some cause opportunistic infections, especially among those w compromised immune systems
- Many affect respiratory system due to inhalation of spores from environment
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Pathogenicity of molds
- varies, but are usually limited to infections of the hair, nails and skin
- includes infections as athlete's foot, jock itch and ringworm
- other infections, usually found in tropical regions, cause moderate to serious infections
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Yeasts
unicellular fungi; important in bread, beer & alcohol production, and other applications
Several species exist as normal flora, especially on mucus membranes and GI tract
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Pathogenicity of yeast
- Some species are opportunistic pathogens of humans which take advantage of weakened defenses
- Most common caused by Candida albicans which causes thrush (infection of mouth and pharynx) & vaginitis
- Those w diabetes & compromised immune systems most susceptible, systemic infections do occur
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Parasitic organisms, classification
- two large groups: single-celled protozoa & multi-celled helminths (worms)
- Protozoa are in kingdom Protista
- Helminths, like humans, are in kingdom Animalia
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parasite
- an organism that lives at the expense of another organism
- transmitted to humans by vectors ~ biologically, ex: mosquito transmitting malaria. ~ mechanically, Ex: transmission of parasite eggs to food by flies & other insects
- endemic to much of worlds population, especially in underdeveloped countries
- account for up to 20 million deaths per year, either from parasitic disease itself, or from complications from disease
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Protozoa
- single-celled, in kingdom Protista
- in general, 2 stages: trophozoite & cyst stage
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Trophozoite stage
protozoa stage which is infective; the motile, invasive form of the organism
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Cyst stage
protozoa stage which allows the organism to survive in a dormant state in the external environment
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Giardia lamblia
- very common protozoan disease for humans, found worldwide
- Humans become infected by ingesting the cysts in water contaminated by animal carriers
- a flagellated protozoan causing intense gastrointestinal distress & diarrhea
- can be treated w antibiotics
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Cryptosporidium
- common protozoan pathogenic for humans
- become more prevalent
- causes self-limiting GI symptoms
- Infected individuals can become chronic carriers, potentially have ability of infecting others
- associated with recreational water use (public swimming pools)
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Plasmodium
- common pathogenic protozoan for humans, who are intermediate hosts
- causes malariafirst goes after liver, next generation affects red blood cells
- causes over 1 million deaths per year, most are young children in Africa
- several species, all transmitted by Anopheles mosquito
- organism invades RBC's during asexual phase of life cycle
- can't survive in humans w sickle-cell disease
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Helminths
- (Worms)
- come in four groups: flukes, tapeworms, roundworms and tissue parasites (which can be a roundworm, larval form or tapeworm)
- hosts are definitive or intermediate, or accidental
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definitive hosts
host for helminth which harbor the parasite when it reproduces by sexual reproduction
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intermediate hosts
hosts for helminth which harbor the parasite at some developmental stage in it's life cycle
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Accidental hosts
- hosts for helminth which are not part of the normal life cycle of the infectious parasite
- most are also 'dead end' hosts, they do not transmit the infection further
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Examples of helminths
tapeworms and roundworms
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tapeworms
- segmented worms that contain a head (scolex) and many segments (proglottids)
- are hermaphroditic, containing both ovaries and testes
- infective stage is larvae found in cattle and swine
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roundworms
- intestinal, found throughout world.
- Adults live in lumen of intestinal tract
- human infection occurs either by ingestion of mature egg (ovum) or by penetration of skin by larval stages found in warm, moist soil.
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Ascaris
- the giant intestinal roundworms
- "helminths"
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hookworms
can penetrate skin
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Strongyloides
common intestinal worm
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Streptococcus pyogenes
- bacteria that causes pharyngitis
- "strep throat"
- upper respiratory tract infection
- common in winter
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Haemophilus influenzae
- one of top 3 bacterial organisms which can cause pneumonia
- contain a capsule virulence factor
- involved in lower respiratory tract infection (lungs)
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Klebsiella pneumoniae
- one of top 3 bacterial organisms which can cause pneumonia
- contain a capsule virulence factor
- involved in lower respiratory tract infection (lungs)
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Streptococcus pneumoniae
- one of top 3 bacterial organisms which can cause pneumonia
- contain capsule virulence factor
- involved in lower respiratory tract (lungs)
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Salmonella
- type of bacterial organism which infects the GI tract
- acquired from contaminated food or water
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Shigella
- type of bacterial organism which infects GI tract
- acquired from contaminated food or water
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Staphylococcus aureus
- type of bacterial organism which can infect GI tract
- acquired from contaminated food or water
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E. coli 0157:H7
- a specific type of E.coli organism, bacterial
- common in intestinal tract of cattle, has been linked to contaminated meats and veggies
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Haemophilus Influenzae
- type of bacterial organism which infects the cerebrospinal fluid and meninges
- particularly in young children
- vaccine is available
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Neisseria meningitidis
- type of bacterial organism with infects the cerebrospinal fluid and meninges
- particularly in young adults
- vaccine is available
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Clostridium botulinum
- botulism
- secretes toxins
- bacterial
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Clostridium tetani
- tetanus
- secretes toxins
- bacterial
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Staphylococcus aureus
- toxic shock syndrome
- secretes toxins
- bacterial
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Candida albicans
- species of yeast that cause the most common yeast infections
- causes thrush in the mouth and vaginitis
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