Microbiology Overview

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Microbiology Overview
2011-01-20 23:33:09
Microbiology Overview PHPR523

Microbiology Overview
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  1. What is the cell wall of a prokaryote made of?
    • proteins
    • lipids
    • peptidoglycans
  2. What function does peptidoglycan serve?
    • provides rigidity
    • determines the shape of the bacteria
  3. What is the difference between the peptidoglycan of gram-positive and gram-negative bacteria?
    very few cross-linkages in gram-negatives
  4. What dyes are used to classify gram-positive bacteria?
    • crystal violet
    • iodine
  5. What dyes are used to classify gram-negative bacteria?
  6. What is the gram-negative cell envelope made of?
    • lipopolysaccharides
    • lipoproteins
  7. Which type of differential media doesn't allow gram-positive bacteria to grow?
    MacConkey agar

    • supports growth of coliform bacteria
    • differentiates lactose fermentors
  8. What bacteria does Thayer-Martin medium allow to grow?
    Neisseria only
  9. What use does CHROM agar have?
    differentiates between Candida species
  10. What is a coagulase test?
    • tests for an extracellular protein that binds to prothrombin to form staphylothrombin
    • Only S. aureus is coagulase positive
  11. What is a catalase test?
    • distinguishes between streptococci and staphylococci
    • strep is catalase negative
    • staph is catalase positive
    • determined by dropping hydrogen peroxide on a colony (bubbling indicates a positive result)
  12. What is the purpose of the Lancefield serogroup test?
    to group various streptococcal species based on serologic reactivity of the cell wall polysaccharide
  13. What bacteria are anaerobic?
    • bacteroides
    • clostridium
    • peptostreptococcus
    • fusobacterium
    • prevotella
    • propionibacterium
  14. What bacteria are gram-negative?
    • moraxella
    • neisseria
    • chlamydia
    • bordetella
    • brucella
    • campylobacter
    • francisella
    • helicobacter
    • hemophilus
    • legionella
    • citrobacter
    • enterobacter
    • escherichia
    • klebsiella
    • morganella
    • proteus
    • providencia
    • salmonella
    • serratia
    • shigella
    • acinetobacter
    • burkholderia
    • pseudomonas
    • stenotrophomonas
    • pasteurella
    • vibrio
    • bacteroides
    • fusobacterium
    • prevotella
    • pneumococcus
  15. What bacteria are gram-negative anaerobes?
    • bacteroides
    • fusobacterium
    • prevotella
  16. What bacteria are spiral organisms?
    • borrelia
    • leptospira
    • treponema
  17. What bacteria is facultative?
    S. aureus
  18. What is alpha hemolysis?
    • partial hemolysis
    • produces a small clear zone on blood agar
    • S. pneumoniae
    • Viridans gp streptococci
  19. What is beta hemolysis?
    • complete hemolysis
    • produces a large clear zone on blood agar
    • S. pyogenes (A)
    • S. agalactiae (B)
    • S. bovis (D)
    • Enterococcus
  20. What is gamma hemolysis?
    • no hemolysis
    • no clear zone on blood agar
  21. What types of biochemical tests are used to differentiate bacteria?
    • coagulase test
    • catalase test
    • Lancefield serogroup test
    • oxygen requirements
    • respiration
    • hemolysis
  22. What is serologic testing?
    testing the host for antibodies against the pathogen
  23. What bacteria are serologic tests available for?
    • Legionella pneumophila
    • Treponema pallidum
    • Chlamydia psittaci
    • Chlamydia pneumoniae
    • Chlamydia trachomatis
    • Mycoplasma pneumoniae
  24. What is genetic testing for bacteria?
    DNA probe hybridization (single-stranded DNA probes bind to complementary rRNA of target microbes)
  25. What bacteria can be tested for using genetic testing?
    • Chlamydia trachomatis
    • neisseria gonorrhoeae
    • Coccidioides immitis
    • Histoplasma capsulatum
    • Blastomyces dermatitidis
    • Mycobacterium tuberculosis
    • Mycobacterium avium complex
  26. What bacteria grow in clusters of gram-positive cocci?
  27. What bacteria grow in chains of gram-positive cocci?
  28. What bacteria grow in pairs of gram-positive cocci (diplococcus)?
    • Enterococcus
    • Pneumococcus
  29. What bacteria are gram-positive bacilli?
    • Bacillus
    • Corynebacterium
    • Gardnerella
    • Actinomyces
    • Lactobacillus
    • Listeria
    • Nocardia
    • Rhodococcus
  30. What bacteria are gram-negative bacilli?
    • Escherichia
    • Klebsiella
    • Enterobacter
    • Serratia
    • Citrobacter
    • Proteus
    • Providencia
    • Morganella
    • Salmonella
    • Shigella
    • Enterobacteriaceae
    • Aeromonas
    • Vibrio
    • Pasteurella
    • Pseudomonas
    • Acinetobacter
    • Haemophilus
    • Campylobacter
    • Legionella
  31. What bacteria are coliform gram-negative bacilli?
    • Escherichia
    • Klebsiella
    • Enterobacter
    • Serratia
    • Citrobacter
  32. What bacteria are non-coliform gram-negative bacilli?
    • Proteus
    • Providencia
    • Morganella
    • Salmonella
    • Shigella
  33. What bacteria are gram-negative bacilli fermentors?
    • Enterobacteriaceae
    • Aeromonas
    • Vibrio
    • Pasteurella
  34. What bacteria are gram-negative non-fermentors?
    • Pseudomonas
    • Acinetobacter
  35. What bacteria are fastidious gram-negative bacilli?
    • Haemophilus
    • Campylobacter
    • Legionella
  36. What bacteria are gram-negative cocci?
    • Moraxella
    • Neisseria
  37. What bacteria are atypical?
    • Chlamydia
    • Mycoplasma
    • Legionella
  38. What makes Chlamydia atypical?
    cell wall is similar to gram-negatives, but no peptidoglycan present
  39. What makes Mycoplasma atypical?
    no cell wall
  40. What makes Legionella atypical?
    • gram-negative, but difficult to stain
    • difficult to grow on standard media
  41. Which fungi are unicellular?
  42. How do yeasts reproduce?
    blastoconidia formation or fission (budding)
  43. What fungi form hyphae?
  44. What type of hyphae penetrate medium (grow down)?
    vegetative hyphae
  45. What type of hyphae grow upward and bear reproductive bodies?
    aerial hyphae
  46. What fungi are yeasts?
    • Candida
    • Cryptococcus
  47. What fungi are moulds?
    • Tinea
    • Aspergillus
  48. What fungi are dimorphic?
    • Blastomyces
    • Histoplasma
    • Coccidioides
  49. What is a conidiophore?
    the stem of an aerial hyphae
  50. What is a phialide?
    row of cells along the vessicle of an aerial hyphae
  51. What is a conidia?
    a bud of an aerial hyphae
  52. What is the Minimum Inhibitory Concentration (MIC)?
    the lowest concentration required to inhibit the visible growth of an organism
  53. What is the Minimum Bactericidal Concentration (MBC)?
    the lowest concentration required to kill 99.9% of colony forming units
  54. What is tolerance?
    when the MBC is 4-8x greater than the MIC
  55. How long does it take to determine an MIC?
  56. How long does it take to determine an MBC?
  57. What are the methods for determining an MIC?
    • macro-bath dilution
    • micro-broth dilution
    • agar dilution
    • Kirby-Bauer disk-diffusion
    • epsilometer strip ("E test")
    • automated systems
  58. Why is a true MIC rarely determined?
    • dilutions are performed by doubling:
    • 0.5, 1, 2, 4...
    • an MIC of 4:
    • actually somewhere between 2 and 4
  59. What are the limitations of MICs?
    • don't provide information regarding rate or extent of killing
    • conducted with a standard inoculum
    • media does not contain plasma proteins or complement
    • don't take site of infection into account (affects drug penetration, distribution, and protein binding)
  60. What is the advantage of time-kill curves?
    • rate and extent of killing can be determined
    • regrowth can also be determined
  61. How is a time-kill curve determined?
    • broth is inoculated with a test isolate at a standard inocula and a known amount of antibiotic
    • samples are removed from the testing containers at predetermined time-points and plated on agar
  62. What is virulence?
    a quantitative measure of pathogenicity or the likelihood that it will cause disease
  63. What are virulence factors?
    factors that enable a microbe to establish itself on or within a host and enhance its potential to cause disease
  64. What is a primary pathogen?
    • regularly cause disease in susceptible individuals with apparently intact defense systems
    • S. aureus
    • S. pneumoniae
  65. What is a secondary pathogen?
    • cause disease more readily in individuals with underlying chronic disease or in those otherwise compromised
    • P. aeruginosa
    • C. albicans
  66. What must a pathogen do to cause disease?
    • colonize the host
    • gain access to the host (break down defenses or wait for trauma)
    • find a niche within the host
    • evade host defenses
    • multiply within the host
  67. How do microbes adhere to the host?
    • fimbriae/pili
    • lectins
    • lipids
    • mechanical
  68. What is a biofilm?
    • matrix-enclosed bacterial populations that adhere to a surface, interface, and each other
    • increase resistance to microbials
    • help evade host defenses
    • P. aeruginosa
    • S. epidermidis
  69. What are the mechanisms used to evade host defenses and remain viable?
    • production of antiphagocytic capsule
    • production of toxins
    • production of destructive enzymes
    • stealth
  70. What is a antiphagocytic capsule?
    • polysaccharide capsules discourage antibody recognition and retard complement fixation
    • N. meningitidis
    • S. agalactiae (B)
  71. What are toxins?
    • diverse microbial products that allow the pathogen access to their niche in the host
    • provide a means for environmental signaling between bacteria
    • protect the bacteria from clearance by the host
    • many are actually enzymes with specific intracellular targets within host cells
    • often comprised of a binding domain (B subunit) and an enzymatic domain (A subunit) that is responsible for the toxic effects once inside the cell
  72. What are the two major types of toxins?
    • endotoxin
    • exotoxin
  73. What is an exotoxin?
    • bacterial products that are protein in nature
    • released by the bacterium during exponential growth
    • toxic to target cells
  74. What is an endotoxin?
    • intracellular
    • cell-associated toxic components of gram-negative bacteria
  75. How are toxins classified?
    • cellular or tissue site of action (tetanus neurotoxin)
    • mechanism of action (adenylate cyclase toxin)
    • intracellular target (protein toxin)
    • major biologic effect (hemolytic toxin)
    • producing organism (cholera toxin)
  76. What is the most common type of toxin?
    • lipopolysaccharides
    • membrane bound virulence factor produced by some gram-negative bacteria
    • commonly referred to as LPS or endotoxin
    • triggers humoral enzymatic mechanisms involving the complement, clotting, fibrinolytic, and kinin pathways
  77. How are bacterial genetic materials transferred?
    • bacteriophages
    • plasmids
    • transposons
    • transformation via fragments of chromosomes
  78. What factors contributed to the emergence of antimicrobial resistance?
    • 1. Inappropriate antibiotic use by clinicians:
    • overuse of broad-spectrum agents
    • used for tx of non-bacterial infections
    • inappropriate antimicrobial prophylaxis
    • 2. Lack of patient education or ineffective education:
    • failure to complete regimens
    • non-compliance
    • patient self-medication
    • 3. Widespread antimicrobial use in food production industry
  79. What are the types of antimicrobial resistance?
    • primary
    • secondary
  80. What is primary resistance?
    • naturally occurring
    • prior antimicrobial exposure not required
    • predictable
    • also called inherent, intrinsic, or native
    • E. coli to Vancomycin
  81. What is secondary antimicrobial resistance?
    • develops following antimicrobial exposure
    • not predictable
    • also called acquired
  82. What are the two methods of developing secondary antimicrobial resistance?
    • selection of resistant subpopulations
    • genetic alteration
  83. What are the types of genetic alterations for antimicrobial resistance?
    • spontaneous mutations (point mutations)
    • acquisition of new genetic material
  84. What are the methods of acquiring genetic material for antimicrobial resistance?
    • Conjugation: transfer between bacteria that are in cellular contact
    • Transduction: transfer via bacteriophage (virus)
    • Transformation: uptake and incorporation of exogenous DNA (S. pneumoniae)
  85. What are the types of exogenous DNA that can by used for genetic transformation for antimicrobial resistance?
    • Plasmid-mediated
    • Transposon-mediated
  86. What are the characteristics of plasmid-mediated resistance?
    • extrachromosomal double-stranded DNA (circular)
    • self-replicating
  87. What are the characteristics of Transposon-mediated resistance?
    • DNA fragments
    • relies on host bacteria or plasmids for replication (not self-replicating)
    • intra- or inter-species
  88. What are the mechanisms of antimicrobial resistance?
    • antibiotic inactivating enzymes
    • alteration of target or active site
    • alterations in bacterial cell membranes
  89. What are common antibiotic inactivating enzymes?
    • beta-lactamases
    • aminoglycoside resistance modifying enzymes
    • chloramphenicol acetyltransferase
    • erythromycin esterase
  90. How do beta-lactamases work?
    • split the amide bond of the beta-lactam ring
    • can be constitutive (constant) or inducible
  91. What bacteria have inducible beta-lactamases?
    • Enterobacter
    • Citrobacter freundii
    • Serratia marcescens
    • Pseudomonas aeruginosa
  92. What agents are potent inducers of beta-lactamases?
    • cefotaxime
    • ceftriaxone
    • ceftazidime
    • imipenem
    • clavulanate
  93. What are Extended-spectrum beta-lactamases (ESBLs)?
    • active against all beta-lactams except cephamycins (cefotetan and cefoxitin), cefepime, and carbapenems
    • inhibited by beta-lactamase inhibitors (sulbactam, clavulanate, tazobactam)
    • genes are located on plasmids
    • K. pneumoniae
    • E. coli
  94. What are AmpC-type-beta-lactamases?
    • active against all beta-lactams except cefepime and carbapenems
    • not inhibited by beta-lactamase inhibitors
    • genes found on chromosomes and plasmids
    • may be inducible
    • K. pneumoniae
    • Enterobacter
    • Citrobacter freundii
    • M. morganii
    • Serratia marcescens
    • P. aeruginosa
  95. What are the strategies to overcome beta-lactamase mediated resistance?
    • administer large doses of beta-lactams to overhelm beta-lactamases
    • combine beta-lactams with beta-lactamase inhibitors (tazobactam, clavulanate, sulbactam)
  96. How do aminoglycoside resistance modifying enzymes work?
    • modification as the AG is transported across the cell wall of the microbe
    • commonly observed among Enterococci exhibiting hig-level AG resistance
  97. What targets or active sites are altered for antimicrobial resistance?
    • Penicillin-binding proteins (PBP): S. aureus resistance to beta-lactams
    • Ribosomal binding sites: Strep resistance to gentamicin
    • Cell wall precursors: Enterococcal resistance to vancomycin
    • DNA gyrase: P. aeruginosa resistance to ciprofloxacin
  98. What alterations in bacterial cell membranes cause antimicrobial resistance?
    • porin channels
    • transport proteins
    • efflux pumps
  99. What are porin channels?
    • portals through the bacterial cell wall
    • aqueous interior
    • facilitate transport of hydrophilic molecules into the cell
    • change in number or size can cause resistance
  100. What microbes use efflux pumps?
    • E. coli: TCNs, FQs
    • S. aureus: TCNs, FQs
    • P. aeruginosa: FQs
    • S. pneumoniae: macrolides
    • N. gonorrhoeae: TCNs
    • Candida: azoles
  101. What drugs can be used for MRSA?
    • vancomycin (DOC)
    • bactrim
    • minocycline
    • linezolid
    • daptomycin
  102. What can be used to treat VISA?
  103. What genes convey MRSA and VRSA?
    • mecA
    • vanA
  104. What agents is penicillin-resistant pneumococcus resistant to?
    • PCNs
    • Cephs
    • macrolides
    • bactrim
    • TCNs
  105. What drugs is enterococcus resistant to?
    • cephs
    • bactrim
    • PCNs (static)
    • vancomycin (static)
    • AGs
  106. What genes confer resistance to vancomycin?
    • vanA: inducible, high-level resistance to vanco and teicoplanin
    • vanB: inducible resistance to vanco, susceptible to teicoplanin
    • vanC: constitutive resistance to vanco (may be low level), may be susceptible to teicoplanin
  107. What are the treatment strategies for resistant enterococci?
    • vancomycin, linezolid, daptomycin,a nd streptogramins
    • intermittent vs continuous infusions of beta-lactams and vanco
    • traditional vs once-daily aminoglycosides
  108. What are the strategies for preventing the spread of antibiotic resistance?
    • patient education
    • knowledge of local susceptibility patterns
    • prescriber education
    • develop guidelines for appropriate antimicrobial usage
    • vaccination
    • hand washing