Microbiology Test 2

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  1. Purpose of the streak method
    • To obtain pure cultures from a mixed population of bacteria
    • Separate potential pathogens from normal flora
    • Thinning out microorganisms so individual colonies can be selected
  2. Steps of the streak method
    • Swirl culture to suspend organisms
    • Heat inoculating loop and let cool (kills organisms if too hot), reheat after each quadrant streak to remove remaining bacteria
    • Remove full loop of inoculum without touching the sides of the tube
    • Place loop flat against agar with lid raised just enough to insert loop
    • Streak quadrant 1
    • Turn plate, pass loop through edge of 1st quadrant a few times as you streak the 2nd quadrant
    • Repeat with quadrants 3 and 4.
  3. Purpose of biochemical tests
    • Test for the presence of enzymes
    • Help distinguish between organisms
    • Aid in identification
  4. Genetic material of viruses
    • DNA or RNA, not both
    • Single or double stranded
    • Linear or circular
    • Continuous segment or multiple segments
    • Single strand can be positive sense (like mRNA) or negative sense (needs to be copied to positive before it can be reproduced)
    • Directs the host cell to make new viruses
  5. Capsids of viruses
    • A protein coat on all viruses
    • Genes + capsid = nucleocapsid
    • Made of capsomeres (repeating subunits of proteins)
    • Usually resistant to enzymes/chemicals
    • For protection of the virus
    • Polyhedral: most common, 20 triangular faces and 12 corners (spikes)
    • Helical: ribbon-like with nucleic acid core
    • Complex: not symmetrical, more variety, characteristic of bacteria viruses
  6. Enveloped/Non-enveloped viruses
    • If only a capsid - naked
    • Capsid + envelope = enveloped
    • Matrix proteins between some capsids and envelope that link them together, have a role in assembly
    • Composed of membrane taken as the virus exits the cell
    • Glycoproteins = spikes
    • Common of animal viruses
  7. Function of capsid/envelope
    • Transports and protects genetic material from enzymes/chemicals
    • Provides access to host cells, determines specificity/range
    • Binding, the first step in viral replication (spikes on enveloped, fibers on naked)
    • Enveloped viruses are easier to destroy, if spikes taken away can't attach, alcohol and stomach acids destroy
    • Enteric viruses are non-enveloped, no spikes to remove
  8. Additional features of viruses
    • Matrix proteins in some enveloped
    • Enzymes: - RNA has RNA-dependent RNA polymerase, retrovirus has reverse transcriptase
  9. How viruses are named
    • Structure, chemical composition, similarities in genetic make up
    • Family name ends in viridae
    • Genus name ends in virus
    • Species names usually descriptive or common names
  10. Viral features used to classify viruses
    • Type of genome (DNA or RNA)
    • Morphology (enveloped or not)
    • Genomic characteristics (ss, ds)
    • Replication strategies (retro)
  11. Growing and detecting replication of viruses
    • Have to grow in host cell
    • Have to know the kind of host
    • Lab animals, eggs, tissue culture cells (grow tissues in cultures and then introduce the virus)
    • Replication shows host cell damage (change in cell)
    • Eggs/animals - death, defects, tumors (oncogenic)
    • Cultures - morphology change (cytopathic effect), plaques (clear zones), multinucleate, inclusions, pile ups
  12. Oncogenic/latent viruses
    • Latent: asymptomatic, not producing new viruses, can become reactivated, i.e. human herpesvirus 3, chicken pox → shingles
    • Oncogenic: tumor causing, linked to cancer, papillomavirus & uterine cancer; Epstein-Barr virus; Hepatitis B and liver cancer, DNA and retroviruses become integrated into host cell chromosome
  13. Steps in replication of animal viruses
    • Absorption: binding of the virus to specific sites on the surface of the host cell (capsid proteins or enveloped spikes)
    • Penetration: endocytosis or membrane fusion
    • Uncoating: separating genetic material from the protein coat
    • Synthesis: replication of viral genetic material, protein production or translation, 1 virus in, many out -
    •      proteins made - capsid proteins for ALL, spikes for enveloped, viral enzymes and matrix proteins if needed
    • Assembly: DNA and retrovirus synthesis and assembly usually occur in the nucleus, RNA virus synthesis and assembly usually occur in the cytoplasm
    • Release: non-enveloped cell lysis is most common; enveloped budding is most common
  14. Naming system for RNA and DNA polymerase
    • DNA → DNA : DNA-dependent DNA polymerase (replication)
    • DNA → RNA: DNA-dependent RNA polymerase (transcription)
    • RNA → RNA: RNA-dependent RNA polymerase (virus only)
  15. Basic concepts of viral replication
    • 1 virus in, many out - makes lots of copies
    • Steps to produce many - the virus brings instructions in on its genetic material and takes control of the host cell, uses host cell machinery to replicate
    • Virus uses host cell enzymes, energy, nucleotides, amino acids, ribosomes, tRNA
    • What comes in with the virus must leave with exiting viruses or they are not infectious
    • Spikes for enveloped viruses are inserted into the cell membrane of the host cell at the site where the virus will exit, occurs during assembly.
  16. Replication of DNA viruses
    • The virus only provides the DNA, genetic material
    • Replicated like normal DNA
    • Synthesis and assembly occur in the nucleus of the host cell
    • May become persistent or chronic
    • If incorporated into host DNA, becomes oncogenic
  17. Replication of RNA viruses
    • Instructs the host cell to make RNA-dependent RNA polymerase 
    • Acts like mRNA, once enzyme is made can replicated on our ribosomes
    • Synthesis occurs in the cytoplasm
    • -RNA brings enzyme in its capside to copy to +RNA
    • Retrovirus: RNA copied to DNA by reverse transcriptase, DNA to nucleus, replication: DNA to mRNA, if integrates with host chromosome is now a Provirus, can make viruses (oncogenic) or become latent
  18. How do viruses cause disease
    The virus takes over the cell so the host is not doing its job, malfunction of workforce
  19. Parasite
    An organism that lives at the expense of the host
  20. Definitive host
    The host where the sexual part of the life cycle occurs
  21. Intermediate host
    The host where asexual/larval part of the life cycle occurs, worse off than the definitive host
  22. Vector
    An organism that moves/transmits a parasite from host to host
  23. Biological vector
    • If the parasite lives within the vector then the vector is also a host (transport host)
    • Essential for the spread of a particular disease
  24. Mechanical vector
    Carries the parasite but is not essential for the spread of a particular disease
  25. Why are parasitic diseases often call tropical diseases?
    • Warm climates support parasites/hosts/vectors
    • Malaria - needs the mosquito to move between hosts
    • Poor sanitation in poorer countries brings people into contact with contaminated soils, etc.
    • Hookworm needs warm, moist, well-aerated soil in shade
    • People wear less covering, give more access to organisms
  26. Why are parasitic diseases hard to treat?
    • Eukaryotic, same as human cells so would be targeting self
    • They may have more than 1 host, need to eliminate the reservoir (hookworm living in soil)
    • Complicated life cycles, where to target the vaccine (larva, eggs, adult)
    • Could need annual doses
    • T. Cruzi changes surface coat so new surface antigens every week
    • Hookworm can go dormant in muscle until conditions are favorable.
  27. Characteristics of helminths
    • Multicellular with organ systems
    • Digestive system simple or absent
    • Elaborate reproductive systems
    • 1. Dioecious (male and female)
    • 2. Hermaphroditie (testes/ovaries in 1 worm)
    • 3. All have sexual life cycles (egg, larva, adult)
  28. General life cycle of helminths
    • Adult lays eggs in definitive host
    • Eggs to larva in intermediate host (larval/asexual phase)
    • Larva back to definitive host or will not mature
  29. Phyla of parasitic helminths
    • Roundworms/nematodes - circular
    • Flatworms/Platyhelminthes - flat
  30. Classes of flatworms
    • Flukes: narrowed tail and head, wider body
    • Tapeworms - segmented, look like tape measure
  31. Tapeworm life cycle (Taenia)
    Adult matures in the intestine of the definitive host (human) → eggs released to environment in feces → eggs eaten by grazing animals → larva develops in the small intestine of the intermediate host (cow), moves into tissue and encysts (dormant) → tissue with cyst eaten by definitive host (human) → encysted larva emerges  and develops in the intestine
  32. Fluke life cycle (Schistosoma)
    Eggs shed into water in the feces/urine of the definitive host (human) → eggs hatch and larvae infects water snail (intermediate host) → larva leaves snail and burrows into definitive host → matures, usually in intestinal vessels → mates and lays more eggs
  33. Cysticercosis
    • When larva encysts in muscle, brain, eyes, liver or heart of an intermediate host
    • Humans are accidental intermediate hosts in T. solium tapeworms
    • Acquired when ingest eggs spread in feces
    • Usually in skeletal muscle
    • Commonly produces epilepsy
    • Life threatening if in the brain or eye
  34. Life cycle of roundworm, egg infectious (pinworm)
    • The life cycle is all in one host
    • Eggs ingested → intestines → larva → adult → mate → female migrates to anus and lays eggs at night → eggs transferred to new host or re-infect the same host via fecal-oral route
  35. Life cycle of roundworm, larva infectious (trichinosis, hookworm)
    • Wide range of host (trichinosis)
    • Can go from larva to larva in one host (trichinosis)
    • Wrom matures in intestine → eggs released in feces → larvae hatch and develop in the environment → infection occurs through skin penetration → to intestine to mature (hookworm)
    • Ingestion of larval encysted meat → develop to adults in intestine → mate → eggs → larva develop → cross intestinal wall and form cyst in tissue (trichinosis)
  36. Infectious form of worms
    • Tapeworm: larva "encysted" in meat, T. solium & saginata
    • Fluke: Larva infectious, aquatic intermediate host, liver and blood flukes
    • Roundworm: egg infectious, ascaris & pinworm
    • Roundworm: larva infectious, hookworm & trichinosis
  37. Characteristics of fungi
    • Macroscopic: fleshy fungi (mushrooms)
    • Microscopic: yeast and molds
    • Non-motile
    • Chemoheterotrophs: energy and carbon from organic molecules
    • Molds: prefer aerobic, lower pH environment
    • Yeast: facultative anaerobes, prefer anaerobic environment but can survive in aerobic when stressed
  38. Microscopic fungi
    • Yeast: sing cells, spherical to oval in shape
    • Mold: long, thin, filamentous (hyphae: thread-like cells), non-septate with multinucleate continuous cells, septate with cross-walls, usually have pores to exchange nutrients/organelles
    • Dimorphic: can grow as yeast at body temperature or mold at room temperature
  39. Regions of mold
    • Mycelium: white fuzz, meshwork of intertwined hyphae making up the colony
    • Reproductive hyphae: aerial hyphae, have spores at the end
    • Vegetative hyphae: obtain nutrients and grow, no spores
    • Spores: asexual reproduction
  40. Life cycle of molds
    • Vegetative hyphae → maturing → reproductive hyphae → spores → released to the environment → spore finds favorable environment → germ tube → hypha → surface hyphae
    • Asexual phase: hyphal fragments or asexual spores, arise from reproductive hyphae via mitosis, haploid, rapidly formed in large numbers
    • Sexual phase: spores via meiosis, diploid to all for meiosis, 1N + 1N fuse → 2N, undergo meiosis to make 1N spores, survival and variability, triggered in hard times, more resistant, can remain dormant for long periods, smaller and more darkly pigmented
  41. Fungal mycoses
    • Superficial: Infection on epidermis (hair root, skin, nails) or mucous membrane, usually just irritating, mucous membranes may become systemic (opportunistic) and then becomes fatal
    • Subcutaneous: muscles, fascia, subcutaneous tissues, more serious
    • Systemic: Usually enter by the lungs and spread to other organs, high mortality if immunocompromised, most serious
  42. Ringworm
    • superficial mycosis
    • Caused by dermatophytes
    • As colony grows, the irritating part goes to the outside of the colony and cause the ring-like shape
    • Growth at the tips of the hyphae causes inflammation
  43. Primary pathogen
    • Array of virulence factors
    • Can cause disease in healthy individuals, usually can fight off
    • Deadly if in immunocompromised
    • Usually regionally restricted
    • commonly dimorphic
  44. Opportunistic pathogen
    • Low inherent virulence
    • Not a problem for healthy people
    • Can be a problem for the immunocompromised
  45. Why are fungal infections/diseases hard to treat?
    • Fewer specific targets because eukaryotic cells
    • Long treatment period if spores are present
    • Drug resistance
    • Yeast have capsules, may not activate our immune system
  46. General characteristics of protozoa
    • Single celled
    • Chemoheterotrophs
    • No cell wall, flexibility
    • Aerobic or facultative anaerobes
    • Neutral pH
    • Common near water
    • Motility - cilia, flagella, pseudopods
  47. Trophozoites vs Cysts
    • Trophozoite: motile, feeding stage
    • Cyst: Dormant, highly resistant coat, most enteric infections have
  48. Protozoan cyst importance
    • Allows the organism to survive in the environment between hosts
    • survives stomach acid
    • Trigger to encyst could be dehydration in the colon and a lack of nutrients
  49. Schizogony
    • Asexual reproduction
    • First mitosis produces a multinucleate cell
    • Multinucleate cell undergoes multiple fissions (cell dividing)
    • Common when producing a cyst
    • Virulence: east to multiply/reproduce, 1 cell gives rise to lots of cells
    • Fewer cysts are needed to produce infection
  50. Medical important protozoa
    • Flagellates: non-blood and blood born
    • Ciliates
    • Amoebas: psuedopods
    • Apicomplexans: carried by vectors, not motile
  51. Flagellated protozoa - non-blood born
    • Front flagella
    • Single, spindle-shaped nucleus
    • Asexual reproduction
    • Cyst and non-cyst formers
    • Giardia lamblia: cyst is infectious, human/animal hosts
    • Trichomonis vaginalis: Trophozoite is infectious, humans are only host
  52. Flagellated protozoa - blood born
    • Crescent-shaped cells
    • No cyst
    • Asexual reproduction
    • Spread by the bite of blood-sucking insect vector
    • Can get via blood transfusion, placenta crossover, mother's milk
    • T. Brucei: African sleeping sickness, tropohozoite is infectious, Tsetse fly is vector
    • T. Cruzi: chagas disease, trophozoite is infectious, kissing bug is vector
  53. Amoeba protozoa
    • Cysts are common
    • Asexual reproduction
    • Pseudopodia
    • Entamoeba histolytica: amoebic dysentery (bloody diarrhea), cyst is infectious, humans are the only host
  54. Ciliate protozoa
    • Most form cysts
    • Asexual reproduction
    • Balantidium coli: balantidial dysentery, cyst is infectious
  55. Apicomplexan protozoa
    • Hydrolytic enzymes clustered at the apex
    • Non-motile
    • Intracellular
    • Sexual and asexual phases
    • Multiiple stages of life
    • Oocysts (common) or sporozoites (fewer)
    • Plasmodium species: malaria, sporozoites (trophozoite) infectious, mosquito is definitive host/vector, humans are intermediate hosts
    • Toxoplasma gondii: toxoplasmosis, oocyst is infectious, cat is definitive host, humans are intermediate host if ingest oocyst
Card Set
Microbiology Test 2
Microbiology Test 2
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