Microbiology Overview

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Microbiology Overview
2011-01-11 21:18:49
Microbiology Overview

Microbiology Overview
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  1. What is peptidoglycan and what is the difference in regard to it in G+ vs G- organisms?
    • It is a heteropolymer consisting of N-acetylglucosamine and N-acetylmuramic acid.
    • Provides rigidity and determines shape of bacteria.
    • G+ have many cross-linkages in the peptidoglycan (thick layer)
    • G- have far fewer cross-links (thin layer)
  2. What is the cell wall of prokaryotes composed of?
    • proteins
    • lipids
    • peptidoglycans
  3. What does the cell wall of fungi consist of?
    • chitin
    • mannans & glucans (polysaccharides)
  4. What is the cell membrane of prokaryotes made of?
    • glycoproteins
    • lipids
    • ergosterol
  5. What is a gram-stain used for?
    • To classify bacteria as G+ or G- on the basis of stain retention of cell peptidoglycan
    • G+ stain purple
    • G- stain red
  6. What are 2 different types of media and what do they help determine?
    • Differential - identity of an organism (e.g. MacConkey agar inhibits growth of G+ bacteria and supports growth of G- orgs, esp those that normally grow in the GIT; CHROM agar differentiates betw diff candida spp)
    • Selective - select specific bacteria from mixed cultures (e.g. Thayer-Martin medium allows neisseria to grow)
  7. Purpose of the coagulase test
    differentiates between Staph aureus and other Staph spp (Staph aureus is coagulase positive)
  8. Purpose of the catalase test
    distinguish between streptococci (catalase-negative) and staph (catalase-positive)
  9. Purpose of the lancefield serogroup
    group various streptococcal species
  10. Examples of different oxygen requirements and examples of bacteria that grow under these conditions
    • Aerobic (Pseudomonas aeruginosa)
    • Anaerobic (Bacteroides fragilis)
    • Facultative (S. aureus)
  11. What does a respiration test tell us about bacteria?
    Fermentation tells us if bacteria can utilize glucose or lactose as a substrate. This use produces acid or alcohol. (e.g. Pseudomonas and Acinetobacter are non-fermenting)
  12. What does hemolysis testing tell us about bacteria?
    • If the bacteria is Alpha, Beta, or Gamma
    • Alpha hemolytic do partial hemolysis - clear a small zone (e.g. S pneumoniae, viridans group, streptococci)
    • Beta hemolytic do complete hemolysis - clear a large zone (e.g. S. pyogenes, S. agalactase, enterococci)
    • Gamma have no clear zone (no hemolysis)
  13. What do serologic tests detect?
    • Nonspecific or specific antibodies
    • Presence and quantity can aid in identification of pathogen
    • Tests available for: legionella pneumophila, Treponema pallidum, Chlamydia psittaci, C. pneumoniae, C. trachomatis, Mycoplasma pneumoniae
  14. What are genetic tests/how are they used?
    • DNA probe hybridization: chemiluminescent sigle-stranded DNA probes bind to complementary rRNA of the target microorganism
    • Commonly used to detect Chlamydia trachomatis, neisseria gonorrhoeae, Coccidioides immitis, Histoplasma capsulatum, Blastomyces dermatitidis, Mycobacterium tuberculosis, and Mycobacterium avium complex
  15. If an unknown bacteria is a cluster of G+ cocci, what test might be used to determine the identity?
    • A coagulase test.
    • If + they'd probably be Staph aureus
    • If - they'd probably be Staph epidermidis
  16. If an unknown G+ bacteria is cocci in pairs or chains, what is its likely identity?
    • Streptococci or Enterococcus
    • If they are Streptococci, they could be Alpha or Beta hemolytic.
    • If Alpha, likely identity is S. pneumoniae or Viridans group
    • If Beta, Group A may be S pyogenes, Group B may be S. agalactiae, Group D may be S. bovis, or others
  17. Gram + bacilli are unusual, but what are some of the more likely of this type of bacteria we may encounter?
    • Bacillus spp (B. anthracis)
    • Corynebacterium spp (C. diptheriae)
    • Gardnerella vaginalis
    • Actinomyces spp
    • Lactobabacillus acidophilus
    • Listeria monocytogenes
    • Nocardia spp
    • Rhodococcus equi
  18. Gram - bacilli are usually what type of bacteria?
  19. Name some of the coliform enterobacteriaceae (G- bacilli)
    • E. coli
    • Klebsiella spp
    • Enterobacter spp
    • Serratia marcescens
    • Citrobacter spp
  20. Name some of the non-coliform enterobacteriaceae (G- bacilli)
    • Proteus spp
    • Providencia stuartii
    • Morganella morganii
    • Salmonella spp
    • Shigella spp
  21. Name some G- bacilli that are aerobic and fermentors
    • Enterocacteriaceae
    • Aeromonas hyprophila
    • Vibrio cholerae
    • Pasturella multocida
  22. Name some G- bacilli that are aerobic and non-fermentors
    • Pseudomonas aeruginosa
    • Acinetobacter spp
  23. Name some G- bacilli that are aerobic and fastidious
    • Haemophilus (H. influenzae, H. ducreyi, H. parainfluenzae)
    • Campylobacter jejuni
    • Legionella pneumophilia
  24. Name some aerobic G- cocci
    • Moraxella catarrhalis
    • Neisseria spp (N. gonorrhoeae, N. meningitidis)
  25. Name some G+ anaerobes
    • Clostridium spp (C. botulinum, C. difficile, C. perfringens, C. tetani)
    • Peptostreptococcus spp
    • Propionibacterium acnes
  26. Name some G- anaerobes
    • Bacteroides fragilis (inherently resistant to antibiotics)
    • Prevotella spp
    • Fusobacterium spp
  27. Name 3 atypical bacteria and the reason they're considered atypical
    • Chlamydia spp - cell wall similar to G- but lack peptidoglycan
    • Mycoplasma spp - lack a cell wall
    • Legionella spp - G- but difficult to stain; difficult to grow on standard media; use serologic testing to identify
  28. How are fungi classified?
    According to morphology
  29. Describe yeasts and moulds
    • Yeasts are unicellular and reproduce by formation of blastoconidia or fission (budding)
    • Moulds are characterized by formation of hyphae. Vegetative hyphae penetrate medium and aerial hyphae bear reproductive bodies.
  30. Name some common yeasts
    • Candida spp (C. albicans, C. glabrata, C. krusei, C. lusitaniae, C. parapsilosis, C. tropicalis)
    • Cryptococcus neoformans
  31. Name some common moulds
    • Tinea spp
    • Aspergillus spp (A. flavus, A. fumigatus)
  32. What does dimorphic mean and name some organisms that would be classified as dimorphic
    Can grow as either a yeast or a mould

    • Blastomyces spp
    • Histoplasma capsulatum
    • Coccidioides immitis
  33. Define MIC
    minimum inhibitory concentration - the lowest concentration of an agent that inhibits the visible growth of an organism
  34. Define MBC
    The lowest concentration of an agent that results in a 99.9% reduction in colony forming units
  35. What are three types of tests for the evaluation of antimicrobial activity?
    • MIC/MBC
    • SIT/SBT
    • Time-kill curves
  36. 6 methods for determining MICs
    • 1. Macro-broth dilution
    • 2. Micro-broth dilution
    • 3. Agar dilution method
    • 4. Kirby-Bauer disk diffusion
    • 5. Epsilometer strip method or "E test"
    • 6. Automated systems
  37. What is a MIC50? An MIC90?
    This is the MIC that will inhibit 50% (or 90%) of the population tested
  38. When doubling dilutions (0.5, 1, 2, 4, etc.) if the MIC is read as 4, what is the true MIC?
    It would be somewhere between 2 and 4
  39. Who determines breakpoint values for interpreting MICs and what is it based on?
    • The DCLSI
    • Based on: drug p'kin and p'dyn, distribution of MICs of a population of bacteria, clinical efficacy
  40. What does SIR stand for when talking about breakpoint values?
    • Susceptible
    • Intermediate
    • Resistant
  41. What is an antibiogram?
    A table that tells what percent of a group of bacteria is susceptible to a particular antibiotic
  42. What type of table helps to make formulary decisions regarding antimicrobials and what info is included?
    • An antibiotic susceptibility profile
    • Contains: organism, antimicrobial, MIC50, MIC90, Range, % susceptibility
  43. 5 important points to remember regarding MICs
    • the true MIC is rarely ever determined
    • for a given agent, organisms with low MICs are more likely to be killed than isolates with high MICs
    • MICs don't take site of infx into account, so drug penetration, distribution, and protein binding still need to be considered
    • Studies may publish MIC50 and MIC90 which may be useful for determining agent's overall effectiveness
    • Depts of microbiology publish institutional susceptibility profiles
  44. 3 limitations of MICs
    • Don't provide info regarding rate or extent of killing
    • Conducted with a standard inoculum
    • Media doesn't contain plasma proteins or complement
  45. Define SIT and SBT
    • Serum inhibitory titer and Serum bactericidal titer
    • Analogous to MICs and MBCs
    • AKA Schlicter test
    • Rarely ever performed
  46. Interpretation of SITs and SBTs
    • Larger dilutions have less drug
    • Accounts for individual pharmacokinetics
    • Used to evaluate antimicrobial therapy
  47. What info do time-kill curves provide? How are they performed?
    • Data regarding the dynamics of antimicrobial activity/killing (rate, extent, regrowth)
    • Broth is inoculated with a test isolate at a standard inocula and an known amount of antibiotic. Samples are removed from testing containers at predetermined time-points and plated on agar.
  48. Define pathogen
    any organism capable of causing disease
  49. Define virulence
    a quantitative measure of pathogenicity or the likelihood that an organism will cause disease
  50. Define virulence factors
    the factors that enable a microbe to establish itself on or within a host and enhance its potential to cause disease
  51. What is a principal pathogen?
    a pathogen that can regularly cause disease in susceptible individuals with apparently intact defense systems (e.g. S. aureus, S. pneumoniae)
  52. What is a secondary pathogen?
    a pathogen that can cause disease more readily in individuals with underlying chronic disease or in those otherwise compromised (e.g. P aeruginosa, C. albicans)
  53. What are the 5 steps of bacterial pathogenesis?
    • 1. Colonize the host
    • 2. Gain access to the host
    • 3. Find a niche within the host
    • 4. Evade host defenses
    • 5. Multiply within the host
  54. What are adhesions? Give examples.
    • Microbial structures that mediate adherence or binding of a microbe to the host.
    • fimbriae/pili
    • lectins
    • lipids
    • mechanical
  55. Structures produced by susceptible host cells that microbial adhesions recognize and bind to are called ______.
  56. Adherence to and penetration into host cells may be accomplished via these 3 methods
    • motility
    • chemotactic properties
    • adhesive structures (adhesins)
  57. Purpose of a biofilm
    facilitate binding to target cells (adherence) and elude host defenses and antibiotics (increased resistance to antimicrobials)
  58. What are biofilms?
    matrix-enclosed bacterial populations that adhere to a surface, interface, and each other
  59. Name 2 commonly encountered pathogens which form biofilms
    Pseudomonas aeruginosa and Staphylococcus aureus
  60. What are planktonic bacteria? Sessile bacteria?
    • planktonic - free-floating bacteria
    • sessile - bacteria are adhered to something
  61. 3 mechanisms used to evade host defenses
    • production of an antiphagocytic capsule
    • production of toxins or destructive enzymes
    • stealth
  62. How does the antiphagocytic capsule work to protect the bacteria?
    helps discourage antibody recognition and retard compliment fixation and activation leading to diminished recognition by phagocytic cells
  63. Name 2 bacteria that frequently produce capsules
    • N. meningitidis
    • group B streptococci
  64. How do toxins help bacteria to maintain viability?
    • Allow the pathogen access to their niche in the host
    • Provide a means for environmental signals to be transmitted to other bacteria
    • Protect the bacteria from clearance by the host
  65. What are exotoxins?
    bacterial products that are protein in nature that are released by the bacterium during exponential growth and are toxic for target cells
  66. What are endotoxins?
    intracellular and cell-associated toxic components of G- microbes
  67. True or false: many toxins are actually enzymes with specific intracellular targets within host cells?
  68. What domains commonly make up toxins?
    • Binding domain (B subunit)
    • Enzymatic domain (A subunit) - responsible for toxic effects once inside the cell
  69. How may toxins be classified? Give an example of each.
    • Cellular or tissue site of action (e.g. Tetanus neurotoxin)
    • Mechanism of action (e.g. adenylate cyclase toxin)
    • Intracellular target (e.g. G protein toxin)
    • Major biologic effect (e.g. hemolytic toxin)
    • Producing organism (e.g. Cholera toxin)
  70. What are LPS?
    • lipopolysaccharides or endotoxin
    • membrane-bound virulence factors produced by some G- bacteria
    • triggers humoral enzymatic mechanisms involoving the complement, clotting, fibrinolytic, and kinin pathways
  71. Disease is a byproduct of the _______ and ________ chosen by pathogens for replication and persistence.
    method and site
  72. Within a bacterial species, how many clonal types actually cause disease?
    relatively few
  73. Where are virulence-associated genes commonly located?
    On mobile genetic elements
  74. Genetic material may be transferred via what three ways?
    • 1. transposons
    • 2. bacteriophages
    • 3. plasmids
  75. What is transformation?
    A way in which some bacteria exchange random fragments of their chromosome with other members of their species
  76. What does genetic mobilization allow bacteria to rapidly do?
    adapt to an unfavorable, changing, or new environment