Microbiology Exam 2

• Icosahedral
• Helical
• Complex
• Enveloped
• Naked

• 3-D, 20-sided figure with 12 evenly spaced corners
• Nucleic acid is packed into he center, forming a nucleocapsid

• Have rod-shaped capsomers that bond together to form a series of hollow discs resembling a bracelet
• Discs link with other disc to form a continuous helix into which the nucleic acid strand is coiled

• May have have multiple types of proteins and take shapes that are not symmetrical
• Bacteriophage

• Viruses that posses an additional covering external to the capsid that is usually a modified piece of the host's cell membrane
• Envelope usually has special receptor spikes inserted into it

Viruses that consist of only a nucleocapsid

- RNA --> + RNA --> Proteins or - RNA

• + RNA --> Protein
• + RNA --> - RNA --> + RNA

RNA --> DNA --> Protein

• Adsorption
• Penetration
• Uncoating
• Synthesis
• Assembly
• Release

• Virus attaches to its susceptible host cell by specific binding of its spikes of cell receptors
• Limited host Range

• Virus is engulfed into a vesicle
• Endocytosis: Entire virus engulfed by the cell and enclosed in a vacuole or vesicle
• Fusion: Viral envelope directly fuses with the host cell membrane

• Replication and protein production
• Under the control of viral genes, the cell synthesizes the basic components of new viruses: RNA, molecules, capsomers & spikes
• DNA enters nucleus --> Transcribed into RNA --> Translation into viral proteins --> New DNA synthesized using host nucleotides
• RNA viruses replicated and assembled in the Cytoplasm

Viral spike proteins are inserted into the cell membrane for the viral envelope; nucleocapsid is formed from RNA and capsomers

• Enveloped Viruses bud off of the membrane, carrying away an envelope with the spikes
• Noneveloped and Complex viruses released when they lyses or ruptures

• Virus-induced damage to the cell that alters its microscopic appearance
• Used to identify virus infections
• Inclusion bodies: Compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm
• Syncytia: Fusion of multiple host cells into single large cells containing multiple nuclei

• When viruses enter their host cell and permanently alter its genetic material, leading to cancer (oncoviruses)
• Cells Lose Contact Inhibition:
• Immortalization
• Causes cells to have
• -Increases rate of growth
• -Alterations in chromosomes
• -Changes in the cell's surface molecules
• -Capacity to divide for an indefinite period

Viruses that infect bacteria

• Phage is developing but is not yet infectious
• -Adsorption
• -Penetration
• -Duplication of phage components; Replication of virus genetic material

• virus matures and is capable of infecting a host
• -Assembly of new virions
• -Maturation
• -lysis of weakened cell
• -Release of viruses

• Host chromosome carries bacteriophage DNA
• DNA phages undergo adsorption and penetration into the bacterial host and then enter an inactive prophage stage, during which it is inserted into the bacterial chromosome
• Viral DNA retained by the bacterial cell and copied during its normal cell division so that the cell's progeny will also have the temperate phage DNA

Infectious protein that contains no DNA or RNA

• An abnormal prion protein is acquired via ingestion or mutation
• Infectious protein induces mis-folding or host protein
• -Mis-folded protein can change other proteins
• -Protein plaques and vacuoles harm neurological function

• Mad Cow Disease (Bovine Spongiform Encephalopathy [BSE])
• Cruetzfeld-Jakob Disease
• Variant Creutzfeldt-Jakob
• Kuru

Sum total of genetic material of a cell

Discrete cellular structure composed of neatly packaged DNA molecule

Certain segment of DNA that contains necessary code to make a protein or RNA

Traits created by the expression of the genotype

An organism's distinctive genetic makeup from the sum of all types of genes

• Join Nitrogenous bases
• Weak bonds that are easily broken, allowing the molecule to be unzipped into its complementary strands

Nucleotides bond to form a sugar-phosphate linkage that becomes the backbone of each strand

• Basic unit of DNA structure
• composed of phosphate, deoxyribose sugar and a nitrogenous base

• Purines and Pyrimidines
• Attach by covalent bonds at the 1' position of the sugar
• Spanned the center of the molecule & pair w/ complementary bases from other grands

• Helicase: Unzip the DNA helix
• Primase: Synthesize an RNA primer
• DNA Polymerase III: Add base to new DNA chain; proofread chain for mastakes
• DNA Polymerase I: Remove primer, close gaps, repair mismatches
• Ligase: Final binding of nicks in DNA during synthesis and repair
• Gyrase: Supercoil

• Origins of Replication: Short sequence of rich in A and T held together by only two H-bonds
• Helicases bind to the DNA at the origin
• -Untwist the helix
• -Break the H-bonds
• -Results in two separate strands

• Leading Strand: Synthesized as a continuous, complete strand in 5' to 3' direction
• Lagging Strand: cannot be synthesized continuously due to the opposite orientation (3' to 5')
• -Polymerase adds nucleotides a few at a time in the direction away from the fork (5' to 3')

• Fragments of DNA on the Lagging Strand
• Few nucleotides added at a time in the 5' to 3' direction
• Fork opens & next segment is synthesized backward to point of previous segment
• Fragments attached to the growing end of the lagging strand by DNA Ligase

Master code of DNA is used to synthesize an RNA molecule

• Single-stranded molecule that exists in helical form
• Contains Uracil instead of Thymine
• Sugar in RNA backbone (alternating with phosphate) is Ribose (not Deoxyribose)

• RNA Polymerase: Unwinds the DNA at the promotor
• -Moves along the strand adding complementary nucleotides as dictated by the DNA template, forming the single-stranded mRNA

• Promotor: Region of two sequences of DNA just prior to the beginning of the gene to be transcribed
• Recognized by the RNA polymerase
• Termination Sequence: RNA Polymerase recognizes a code that signals the separation and release of the mRNA strand

• RNA Polymerase runs along the template strand in the 3' to 5' direction
• Elongation proceeds in the 5' to 3' direction
• The mRNA reads in the 5' to 3' direction

• Ribosomes: Located in the cytoplasm
• Subunits specifically adapted to assemble & form sites to hold the mRNA & tRNA
• Recognizes these molecules and stabilizes reactions between them
• tRNA: Brings amino acids to ribosome during translation
• Anticodon that designates the specificity of the tRNA & complements mRNA's codons
• mRNA: Sequence of amino acids in protein
• Carries the DNA master code to the ribosome and then translated

• Initiation
• Elongation
• Termination

• Small subunit binds to the 5' end of mRNA and large subunit supplies enzymes for making peptide bonds on the protein
• Begins to scan the mRNA by moving in the 5' to 3' direction along the mRNA
• The first codon is the START codon (AUG)
• mRNA message in place on the ribosome, tRNA enter with their amino acids
• -Complementary tRNA (anticodon) meets with the mRNA code
• -Guided by the two sites on the large subunit called the P site & A site
• -E site is where the tRNA's are released

• Ribosome shifts its reading frame to the right along the mRNA from one codon to the next
• -Brings the next codon into place on the ribosome and makes a space for the next tRNA to enter the A site
• -Peptide bond is formed between the amino acids on the adjacent tRNA's
• -Polypeptide grows in length
• Translocation: Enzyme-directed shifting of the ribosome to the right along mRNA strand, which causes bland tRNA to be discharged from the ribosome at the E site

• Brought about by the presence of a Termination Codon - UAA, UAG, & UGA
• -No corresponding tRNA (or amino acid)
• -Nonsense Codons
• Special enzyme breaks the bond between the final tRNA and the finished polypeptide chain

A particular amino acid can be coded for by more than a single codon

• Only the first two nucleotides are required to encode the correct amino acid
• -Permits some variation or mutation without altering the message

• Translation of mRNA starts while transcription is still occurring
• Increases efficiency

• Start codon is also AUG but may code for an amino acid (methionine)
• mRNAs code for just one protein
• DNA is in nucleus so transcription and translation cannot be simultaneous
• mRNA must pass through pores in the nuclear membrane and be carried to ribosome's in the cytoplasm
• Introns: Sequences of bases that do not code for protein
• Exons: Coding regions that will be translated into protein (Express)

Coordinated set of genes, all of which are regulated as a single unit

• Operon is turned on by the substrate of the enzyme for which the structural genes code
• -Normally off; Adding Lactose turn it on
• Operon Off: in the absence of lactose, a repressor protein attaches to the operator of the operon
• -Locks the operator & prevents any transcription of the structure gense downstream
• -Supression of transcription prevents the unneccessary synthesis of enzymes for processing lactose
• Operson On: Upon entering the cell, lactose (substrate) becomes a gentic inducer by attaching to the repressor, which loses its grip and falls away
• The RNA polymerase is free to bind to the promotor and initiate transcription

• Contain genes coding for anabolic enzymes
• Several genes in a series are turned off by the product synthesized by the enzyme
• -Normally on; Turned off when the nutrient is not longer required
• Operon On: A repression operon remains on when its nutrient products are in great demand by the cell
• -The repressor is unable to bind to the operator at low nutrient levels
• Operon Off: The operon is repressed when
• -Arginine builds up & serves as a corepressor, activating the the repressor (negative feedback)
• -Repressor complex affixes to the operator and blocks the RNA polymerase and further transcription of genes for arginine synthesis

Microorganisms that bears a mutation (Phenotypic changes due to the changes in the genotype)

Microorganism that exhibits a natural, non-mutated characteristic

• Spontaneous: Random change in the DNA arising from errors in replication that occur randomly
• Induced: Result from exposure to known mutagens (physical or chemical agents that interact with DNA in a disruptive manner)

• Point Mutation: Involve addition, deletion, or substation of single bases
• -May or may not change protein
• Missense Mutation: Any change in code that leads to placement of a different amino acid
• -Can create a faulty, nonfunctional protein
• -Can produce a protein that functions in a different manner
• -Can cause no significant alteration in protein function
• Nonsense Mutation: Changes a normal codon into a stop codon
• Stops the production of the protein wherever it occurs
• Almost always results in a nonfunctional protein
• Silent Mutation: Alters a base but does not change the amino acid
• -Has no effect on the protein function
• Back-Mutation: Gene that has undergone mutation reverses to its original base composition
• Frameshift Mutation: Mutations that occur when one or more bases are inserted into or deleted from a newly synthesized DNA strand
• -Changes the reading frame of the mRNA
• -Nearly always result in a nonfunctional protein

• Enzymatic Enzymes: Special for finding and fixing such mutations; Most common way
• DNA that has been damaged by UV radiation
• -Restored by Photoactivation or Light Repair
• --DNA photolyase- Light sensitive enzyme
• Excision Repair
• -Excise mutations by a series of enzymes
• -Remove incorrect bases and add correct one

When one bacterium donates DNA to another bacterium

• Requires the attachment of two related species and the formation of a bridge that can transport DNA
• -Physical Conjugation: The pilus of donor cell attaches to receptor on recipient cell and retracts to draw the two cells together
• --An opening or pore forms between the cell walls, creating a bridge to transmit genetic material
• -F Factor Transfer: F Factor (plasmid) copies and then transferred though a bridge
• -H factor Transfer: F factor integrated into chromosome and then duplicated and transmitted in part to a recipient cell, where it is integrated into the chromosome

• Entails the transfer of naked DNA and requires no special vehicle
• -Recipient cell takes up donor DNA
• -Donor DNA align with complementary bases
• -Recombination occurs between donor DNA and recipient DNA
• -Griffith's Experiment

• DNA transfer mediated though action of a bacterial virus (bacteriophage)
• Generalized:
• -Random fragments of disintegranting host DNA are taken up the the phage during assembly
• -Any gene from the bacterium can be transmitted
• -Lytic Infection: Lyses the cell to infect others
• --Releases the mature phases, including the genetically altered one
• Specialized:
• -Highly specific part of host genome is regularly incorporated into the virus
• -Lysogenic Infection: Integrated in bacterial chromosome

• Transposable elements
• Shift from one part of the genome to another
• -From one chromosomal site to another
• -From a chromosome to a plasmid
• -From a plasmid to a chromosome
• Contain DNA that codes for the enzymes needed to remove and reintegrate the transposon at another site in the genome
• Overall Effect- Scrambles the genetic language

• Heating to 90^oC separates DNA strands exposing nucleotides
• Cooling to allow annealing
• Complementary strands from different organisms hybridize

• Enzymes that can clip strands of DNA crosswise at selected positions
• Can recognize and clip at Palindromes (Identical sequences of DNA when read from 5' to 3' direction on one strand and the 5' to 3' direction on the other strand)
• Used to cut DNA in to smaller pieces for study or remove & insert sequences
• Can make a blunt cut or a "sticky end"
• Restriction Fragments: The pieces of DNA produced

• Copies made from messenger, transfer, ribosomal and other forms of RNA
• Synthesize eukaryotic genes from mRNA transcripts
• Synthesized gene will be free of the intervening introns

Produces a readable pattern of DNA fragments

• Samples placed in wells in a soft agar gel and subjected to an electrical current
• Phosphate groups in DNA give the molecule an overall negative charge
• -Causes DNA to move toward the positive pole in the gel
• Rate of movement based on size of fragments
• -Larger fragment move slowly and remain near the top of the gel
• -Smaller fragments move faster and positioned farther from the wells
• Positions of DNA fragments determined by staining the DNA fragments in the gel

• Characterize DNA fragments and compare the degree of genetic similarities among samples
• Genetic Fingerprint

• Macrorestriction analysis
• Pathogens isolated from a patient and their DNA is harvested
• -DNA is cut up with restriction enzymes to get a few very large pieces of DNA
• -DNA separated using the pulsed-field method of gel electrophoresis
• --Constantly changes the direction of (pulsing) the electrical field
• --Allows effective separation of the large pieces
• Fragments of different lengths seen as dark bands after special stain on gel
• Patterns different t/t enzyme cut in different places on genome where small DNA changes exist, correspond to different strain types
• DNA Fingerprint

Two different nucleic acids hybridize by uniting at their complementary regions

• Specifically formulated oligonucleotide tracers
• Consists of a short stretch of DNA or a known sequence that will base-pair with a stretch of DNA with a complementary sequence (if in the test sample)
• Carry reporter molecules so areas of hybridization can be visualized

• Type of Hybridization
• DNA fragments are first separated by electrophoresis and then denatured and transferred to a special filter
• DNA probe incubated with the sample
• -Wherever this probe encounters the segment of which it is complementary, it will attach and form a hybrid
• Development of hybridization pattern will show up as one or more bands
• Sensitive and specific way to isolate fragments from a complex mixture and to find specific gens sequences on DNA

• Probes applied to intact cells
• Observed microscopically for the presence and location of specific genetic marker sequences
• Effective way to locate genes on chromosomes

• Determines the actual order and types of bases in DNA
• Sanger Method: Most common technique
• Limitations:
• -Sanger technique is old and expensive (reaching the end of its useful life)
• -May not be specific - None-specific binding of the primer to the DNA

• Rapidly increases the amount of DNA in a sample
• How it is done
• -Denaturation: Heat to separate into two strands
• -Priming: Primers added in a concentration that favors binding to the complementary strand of test DNA
• --Prepares the two strands (amplicons) for synthesis
• -Extension: DNA Polymerase and nucleotides are added to primer
• -Cycling: 20-30 cycles to amplify DNA
• Results: Amplified DNA to be anayzed

• Deliberately removes genetic material from 1 organisms & combines it with that of a different one
• -Forms genetics closes
• --Genes is selected
• --Excise gene
• --Isolate gene
• --Insert gene into a vector
• --Vector insets DNA into a cloning host
• What are the results?
• -Mass produce substances that are difficult to synthesize by the usual industrial methods
• --Hormone, enzymes, vaccines

• Plasmid or virus that a gene is inserted into
• Inserts the DNA into a Cloning Host
• Characteristics
• -Capable of carrying a significant piece of the donor DNA
• -Must be readily accepted by the cloning host
• -Must have a promotor in front of the cloned gene
• -Origin of Replication needed somewhere so that it will be replicated by the DNA polymerase of the cloning host
• -Must accept DNA of the desired size
• -Contain a gene that confers drug resistant to their cloning host

• Bacterium or yeast that can replicate the gene & translate it into the protein product
• Characteristics
• -Rapid turnover, fast growth rate
• -Can be grown in large quantities using ordinary culture methods
• -Nonpathogenic
• -Genome that is well delineated
• -Capable of accepting plasmid or bacteriophage vectors
• -Maintains foreign gene though multiple generations
• -Will secrete a high yield of proteins from expressed foreign genes

Correcting or repairing a faulty gene in humans suffering from a fatal or debilitating disease.

• Bases are complementary to the sense strand of mRNA in the area surrounding the initiation
• -When it binds to the mRNA, the dsRNA is inaccessible to the ribosome
• -Translation cannot occur (stop bad proteins)
• Genetic medicine

• When delivered into the cytoplasm and nucleus, it binds to specific sites on any mRNAs that are the targets of therapy
• -Antisense Therapy: Treat Cytomegalovirus Retinitus

Destroys most microbial life, reducing contamination on inanimate surfaces

Destruction of all microbial life

Same as disinfection except a living surface is involved

Any cleansing technique that mechanically removes microorganisms to reduce contamination to safe levels

• Prions
• Endospores

• Factors that influence the rate at which microbes are killed by antimicrobial agents
• Length of Exposure to Agent
• Effect of the Microbial Load
• Relative Resistance of Spores vs. Vegetative Forms
• Action of the Agent (Microbicidal or Microbiastatic

• Change Membrane permeability
• -Lose selective permeability so can't prevent the loss of vital molecules or stop the entry of damaging chemicals
• Damage the Cell Wall
• -Block its synthesis
• -Digest it
• -Break down its surface
• -The cell becomes fragile and is lysed easily
• Damage Protein
• -denature (disrupt) proteins
• Damage Nucleotides
• -Binding to ribosomes to stop translation
• -Bind irreversibly to DNA preventing transcription and translation
• -Mutagenic agents

• Moist Heat: occurs in the form of hot water, boiling water, or steam
• -Ranges from 60 to 135 Celsius
• Dry Heat: Denotes air with a low moisture content that has been heated by a flame or electric heating coil
• -Ranges from 160 to several thousand degrees of Celsius

• Steam under pressure
• Pressure raises the temperature of steam
• Most efficient pressure-temperature combination for sterilization: 15 psi which yiels 121 degree celsius for 15 minutes

• Heat is applies to liquids to kill potential agents of infection and spoilage *disinfect)
• Maintains the liquids' flavor and food values
• Does not kill endospores or thermoduric microbes
• Does not sterlize

• Disinfection
• Expose material to boilng water for 30 minutes

• Used for heat-resistant items that do not sterilize well with moist head
• -Glass, metallic instruments; powders, oils
• Sterilization

• Ignites and reduces microbes to ashes and gas
• Sterlizes

• Cells' molecules absorb some of the available energy
• Radiation ejects orbital electrons form an atom, causing ions to form
• Gamma Rays, X Rays & Cathode Rays
• Cold sterilization
• Uses
• -Food products
• -Medical products

• Excites atoms by raising them to a higher energy state, but it does not ionize them
• Atomic excitation leads to formation of abnormal bonds within molecules and is a source of mutations
• Not as penetrating as ionizing radiation
• doesn't kill bacterial spores
• Uses
• -Disinfect: Hospital rooms, operating rooms, schools, food prep areas, dental offices
• -Treat drinking water or purify liquids

• Mechanical technique for removing microbes
• Effective for removing microbes from air and liquids
• Fluid strained through a filter with openings large enough for fluid but too small for microorganisms
• Filters are usually thin membranes of cellulose acetate materials
• Pore size can be standardized
• Prepare liquids that can't withstand heat
• Can't decontaminate beverages without altering their flavor
• Water purification
• Removing airborne contaminants (HEPA filters)

• Halogen - betadine; Bleach
• Phenol- Listerine; Lysol
• Chlorhexadine- Avagard
• Alcohols- Hand sanitizer
• Hydrogen Peroxide
• Detergents- Soaps
• Heavy metal compounds- Mercury; Silver; Silver nitrate
• Aldehydes- Glutaraldhyde; Formaldehyde

• Halogen- Yes
• Phenol- No
• Chlorohexadine- Yes (had scrubbing, preparing skin for surgery, neonatal wash)
• Alcohols- Yes
• Hydrogen peroxide- Yes
• Heavy metals- Yes (topical)
• Aldehydes: No
• Gases
• -Ethylyne Oxide- No
• -Hydrogen Peroxide- No
• Dyes- Yes

Use of a drug to prevent imminent infection of a person at risk

Substances produced by the natural metabolic processes of some microorganisms than can inhibit or destroy other microorganisms

Antimicrobial effective against a limited array of microbial types (e.g., gram-positive bacterial)

Antimicrobial effective against a wide variety of microbial types (e.g., both gram-positive and gram-negative bacteria)

• Inhibition of Cell Wall synthesis
• Inhibition of Nucleic Acid Structure and Function
• Inhibition of Protein Synthesis
• Interference with Cell Membrane Structure or Function
• Inhibition of Folic Acid Synthesis

• Bind and block peptidases that cross-link the glycan molecules
• Interrupts the completion of the cell wall

• Resistant to most beta lactamases (penicillinases)
• Cause fewer allergic reactions than penicillins

• Catalyze cross-linking of peptidoglycan chains
• Penicillin must bind to them to produce antibacterial effects

• Involved in different stages of bacterial cell wall synthesis
• When one type is inhibited, it inhibits the specific stage of peptidoglycan synthesis

Enzymes that are cable of destroying the beta-lactam right of penicillin

Vancomycin (Important for treating MRSA)

• List of Actions
• -Block synthesis of nucleotides
• -Inhibit replication
• -Stop transcription
• -Inhibit DNA synthesis
• Metronizadole for parasites

• Inhibit translation by reacting with the ribosome-mRNA comlex
• Classes of Antibiotics
• Aminoglycoside
• Tetracyclines
• Oxazolidonones
• Chloramphenicol
• Macrolides
• Licosamides
• Quinolones
• Stretogramins

• Disruption in metabolism
• Polymyxin B

• Supplied to cells in high concentrations to make sure enzyme is constantly occupied with the metabolic analog rather than the true substrate
• Sulfonamides and Trimethoprim: Competitive Inhibition

• Macrolide Polyene Antibiotics
• -Bind to fungal membranes and cause loss of selective permeability
• Griseofulvin
• -Especially active Skin fungal infections
• Synthetic Azoles
• -Broad spectrum antifungal agents
• -Ketaconazole, fluconazole,...
• Flucytosine
• -Can be used to treat certain cutaneous mycoses

• Some also antibiotics
• Metronizadole (Flagyl)

Selective toxicity is almost impossible to achieve because a single metabolic system is responsible for the well-being of both virus and host

• Barring penetration of the virus into the host cell
• Blocking the transcription and translation of viral molecules
• Preventing the maturation of viral particles

• Glycoprotein produced by fibroblast and leukocytes in response to various immune stimuli
• Produced by recombinant DNA technologies
• Known therapeutic benefits:
• Reducing the time of healing and some of the complications in certain infections
• Prevent or reducing some symptoms of cold and papilomaviruses
• slowing the progress of certain cancers
• Treating a rare Cancer called hairy-cell leukemia, hepatitis C, genital warts, and Kaposi's sarcoma in AIDS patients

• Drug Inactivation
• -Due to now enzymes being synthesized
• -Beta lactamases
• Decreased Permeability
• -Activation of Drug pumps: Uptake of drug into bacterium is decreased/eliminated
• Change in Drug binding site
• -Binding sites decreased in number or affinity
• -Mec A
• Use of Alternate metabolic pathway
• -Affected metabolic pathway shut down or an alternate pathway is used

• Toxic
• Allergies
• Suppression of normal flora
• Superinfection
• -Complication that occurs when antimicrobial therapy destroys beneficial resident species, causing microbes that were once in small numbers begin to overgrown and cause disease
• C. difficile example
• -Oral therapy with tetracycline, clindamycin, and broad-spectrum PCN and cephalosporins is associated with antibiotic-associated colitis due to C. Difficile

• Uses a strip to produce a zone of inhibition
• Strip contains a gradient of drug calibrated in micrograms
• MIC can be measured by observing the mark on the strip that corresponds to the edge of the zone of inhibition

• Agar diffusion test that provides useful data on antimicrobial susceptibility
• Surface of a plate of special medium is spread with the test bacterium
• Small disc containing a premeasured amount of antimicrobial dispensed onto bacterial lawn
• Zone of inhibition surrounding disc measured and compared with a standard for each drug
• Profile of antimicrobial sensitivity provides data for drug selection

• Smallest concentration (highest dilution) of drug that visibly inhibits growth
• Useful in determining the smallest effective dosage of drug & in providing a comparative index against other antimicrobials

• The inability of the drug to diffuse into that body compartment
• A few resistant cells in the culture that did not appear in the sensitivity test
• An infection caused by more than one pathogen, some of which are resistant to the drug

Capable of causing disease in healthy person with normal immune systems

Cause disease when the host's defenses are compromised or when they become established in part of the body that is not natural to them

Infections that come on rapidly, when severe but short-live effects

Infection that progress and persist over a long period of time

Inapparent, asymptomatic

• Describes the degree of pathogenicity
• -Determined by its ability to
• --Establish itself in the holt
• --Cause damage

A route in which the microbe enters the tissues of the body

• Comes across the placenta and invade the fetal circulation
• Considered a vertical transmission

• How many organisms need to make 50% of people sick
• How does it affect Virulence?
• -Microorganisms with smaller IDs have greater virulence