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STEP 1 Microbiology > General- Bacteria and antibiotics > Flashcards

General- Bacteria and antibiotics Flashcards

1
Q

Yersinia- morphology

A

Gram-negative coccobacilli;

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2
Q

Yersinia pestis- transmission

A

Rodents (currently prairie dogs) are reservoir, spread to humans by fleas (vector).

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3
Q

Yersinia pestis- presentation

A
  • Bubonic plague (buboes form on skin)
  • Abscesses in organs
  • DIC due to endotoxin
  • Cutaneous hemorrhage
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4
Q

Yersinia pestis- virulence

A
  • Endotoxins (cause DIC)
  • Exotoxins
  • Yersinia-associated outer proteins (YOPs) that inhibit phagocytosis and cytokine production
  • Type III secretion system (injectisome) spreads YOPs
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5
Q

Yersinia pestis- treatment

A

Aminoglycosides (streptomycin) + tetracycline

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6
Q

Yersinia pestis- vaccine

A

Killed vaccine

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7
Q

Streptococcus pneumoniae- morphology

A

Lancet-shaped Gram-positive diplococci; alpha-hemolytic, encapsulated, Optochin sensitive, bile soluble

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8
Q

Streptococcus pneumoniae- presentation

A

“MOPS”

  • Meningitis
  • Otitis media
  • Pneumonia (lobar with rust-colored sputum)
  • Sinusitis
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9
Q

Streptococcus pneumoniae- virulence

A

IgA protease for mucosal invasion

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10
Q

Why are patients with sickle cell disease/asplenia susceptible to Strep pneumo?

A

Encapsulated organism; spleen removes these from the body

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11
Q

Streptococcus pneumoniae- treatment

A

Macrolides (azithromycin) or ceftriaxone

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12
Q

Streptococcus pneumoniae- vaccine

A

1) Adult- 23-valent polysaccharide (no protein; T-cell independent that creates IgM)
2) Children- 7-valent conjugated to protein (T-cell response generated with IgG)

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13
Q

Role of pilus/fimbria

A

Adherence and sexual reproduction

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14
Q

Gram negative cell wall properties

A

Thin peptidoglycan cell wall with two membranes. Outer membrane has LPS and porins. Inner cell membrane is within the cell wall.

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15
Q

Gram positive cell wall properties

A

Thick peptidoglycan wall with lipoteichoic acid and teichoic acid

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16
Q

Mycobacteria cell wall properties

A

Thin peptidoglycan covered in arabinoglycan and wall with mycolic acids at the outer surface

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17
Q

Common cocci (and Gram staining)

A
  • Gram-positive: Staphylococcus, Streptococcus, Enterococcus
  • Gram-nergative: Moraxella, Neisseria
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18
Q

Common bacilli (and staining)

A
  • Gram-positive: Bacillus, Clostrioidium
    , Listeria, Lactobacillus, Mycobacterium
  • Gram-negative: Enterobacteriaceae
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19
Q

Common branching/filamentous bacteria

A

Nocardia, actinomyces

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20
Q

“Beaded branching positive rod”

A

Nocardia, actinomyces, aerobic actinomycetes

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21
Q

Common pleomorphic bacteria

A

Chlamydiae, Mycoplasma, Ureaplasma, Anaplasma/Ehrlichia

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22
Q

Common spiral bacteria

A

Borrelia, Leptospira, Treponema

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23
Q

“Gram-variable coccobacillus”

A

Acinetobacter

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24
Q

How is Gram staining done?

A
  • Apply crystal violet (stain)
  • Apply iodine (mordant, forms complex with crystal violet)
  • Apply alcohol (degrades thin Gram-negative cell wall and allows CV-I complex to leak out)
  • Now, only Gram-positive organisms are purple
  • Counterstain with safranin for Gram-negative organisms
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25
Q

Species that do not Gram stain well due to size

A

Treponema, Leptospira

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26
Q

Species that do not Gram stain well due to impermeable cell wall

A

Mycobacteria (appear as beaded, branching rods)

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27
Q

Species that do not Gram stain well due to a lack of cell wall

A

Mycoplasma, Ureaplasma

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28
Q

Species that do not Gram stain well due to intracellular location

A

Chlamydia, Rickettsia, Coxiella

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29
Q

What does Ziehl-Neelsen stain show?

A

Acid fast Bacilli (Mycobacterium species) and protozoa

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30
Q

How is a Ziehl-Neelsen stain performed?

A
  • Application of carbolfuchsin (stain)
  • Application of heat (mordant)
  • Application of acid alchohol
  • Now acid-fast bacteria are pink
  • Counterstain non-AFB with methylene blue
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31
Q

What does it mean to be partially acid fast?

A

They can hold the Carbolfuchsin stain with a less strong acid wash

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32
Q

What are some partially acid-fast organisms?

A

Nocardia, Gordonia

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33
Q

What is the role of bile salts when used in McConkey agar?

A

Selective; Allows growth of most Gram-negative rods but inhibits most Gram-positive organisms

34
Q

What is the role of lactose and phenol red (indicator) in McConkey agar?

A

Differential; Lactose fermenters turn the colony and agar pink, while non-lactose fermenters remain colorless

35
Q

How is Haemophilus influenzae cultured?

A

Chocolate agar with Factors V (NAD+) and X (hematin)

Not Roman numerals

36
Q

How is Neisseria cultured?

A

Thayer-Martin agar, which includes vancomycin (inhibits Gram-positive), Trimetoprim and colistin (inhibit Gram-negatives), and Nystatin (inhibits yeast)

37
Q

How is Bordetella pertusis cultured?

A

Regan-Lowe agar, which includes charcoal, blood, and antibiotics

38
Q

How is TB cultured?

A

Lowenstein-Jensen agar, which is rich and includes egg yolk and lipids (needed for mycolic cell wall); slow-grower

39
Q

How is Legionella pneumophila cultured?

A

Charcoal yeast extract buffered with cysteine and iron (BCYE)

40
Q

Examples of obligate aerobes

A

Nocardia, pseudomonas aeruginosa, and mycobacterium

41
Q

Why is oxygen toxic to anaerobes?

A

They lack catalase and/or superoxide dismutase and are susceptible to oxidative damage

42
Q

Examples of obligate anaerobes

A

Clostridium (except perfringens), Bacterioides, Fusobacterium, and Actinomyces

43
Q

Examples of facultative anaerobes

A

Streptococcus, Staphylococcus, and enteric Gram-negative rods

44
Q

Examples of facultative intracellular bacteria

A

Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis

45
Q

Examples of encapsulated bacteria

A

Pseudomonas, Strep pneumo, H. flu, Neisseria meningitidis, E. coli, Salmonella, Klabsiella, Group B Strep

46
Q

Who is at particularly high risk for infection with encapsulated organisms?

A

Asplenic patients

47
Q

How do cultures appear with an encapsulated bacteria?

A

Wet, mucoid

48
Q

Urease-posive bacteria

A

Proteus, Heliobacter pylori, Ureaplasma, Nocardia, Klebsiella, Staph epidermidis, Staph saprophyticus

49
Q

Catalase-positive bacteria

A

Heliobacter pylori, Nocardia, Staphylococcus, E. coli, Burkholderia cepacia

50
Q

Blue-green pigment- producing bacteria

A

Pseudomonas (may also make red pigment)

51
Q

Gold-yellow pigment-producing bacteria

A

Staphylococcus aureus

52
Q

Red/pink pigment-producing bacteria

A

Serratia marcescens

53
Q

Purple pigment-producing bacteria

A

Chromobacterium violaceum

54
Q

Examples of biofilm-producing bacteria

A

Steph epidermidis, Strep viridans, Pseudomonas

55
Q

Where is Staph epidermidis frequently observed?

A

Catheter and prosthetic device infections

56
Q

Where is Strep viridans frequently observed?

A

Dental plaques and infective endocarditis

57
Q

Examples of spore-forming bacteria?

A

Bacillus (anthracis and cereus), Clostridium (botulinum, difficile, perfringens, tetani)

58
Q

Bacteria with exotoxins that inhibit protein synthesis (and name of toxin)

A
  • Diptheria (diptheria toxin)
  • Pseudomonas (exotoxin A)
  • Shigella (shiga toxin)
  • EHEC (shiga-like toxin)
59
Q

Bacteria with exotoxins that increase fluid secretion (and name of toxin)

A
  • ETEC (heat-labile and heat-stable toxins)
  • Bacillus anthracis (edema toxin)
  • Vibrio cholerae (cholera toxin)
60
Q

Bacteria with exotoxins that inhibit phagocytosis (and name of toxin)

A
  • Bordatella pertusis (pertussis toxin)
61
Q

Bacteria with exotoxins that inhibit neurotransmitter release (and name of toxin)

A
  • Clostridium tetani (tetanospasm)

- Clostridium botulinum (botulinum toxin)

62
Q

Bacteria with exotoxins that lyse cell membranes (and name of toxin)

A
  • Clostridium perfringens (alpha toxin)

- Strep pyogenes (streptolysin O)

63
Q

Bacteria with super-antigens causing shock

A
  • Staph aureaus (toxic shock syndrome toxin)

- Strep pyogenes (erythrogenic exotoxin A)

64
Q

What test can be used to classify Gram-positive cocci?

A

Catalase test.

  • Positive => Staph
  • Negative => Strep (or enterococcus)
65
Q

What test can be used to classify alpha-hemolytic Streptococci?

A

Optochin sensitivity.

  • Yes => Strep pneumo (capsule)
  • No => Viridans strep (no capsule)
66
Q

What test can be used to classify beta-hemolytic Streptococci?

A

Bacitracin sensitivity.

  • Yes => Strep pyogenes (group A)
  • No => Strep agalactiae (group B)
67
Q

Which type of Streptococcus is “group A strep”?

A

Streptococcus pyogenes

68
Q

What test can be used to classify gamma-hemolytic Streptococci?

A

Growth in 6.5% NaCl.

  • Yes => Enterococci (group D)
  • No => Strep bovis
69
Q

What test can be used o classify Staphylococci?

A

Coagulase test.

  • Positive => Staph aureus
  • Negative => Staph saprophyticus OR epidermidis
70
Q

What test can be used to classify coagulase-negative Staphylococci?

A

Novobiocin sensitivity.

  • Yes => Staph epidermidis
  • No => Staph saprophyticus
71
Q

Gram-positive aerobic bacilli

A

Listeria, Bacillus, Corynebacterium

72
Q

Gram-positive anaerobic bacilli

A

Clostridium

73
Q

Gram-positive aerobic bacteria with branching filaments

A

Nocardia (weakly acid fast)

74
Q

Gram-positive anaerobic bacteria with branching filaments

A

Actinomyces (not acid fast)

75
Q

What is observed in mass spec for bacteria?

A

16S ribosomal protein components

76
Q

What is the mecA marker, and where is it observed?

A

Encodes methicillin-resistant PBP2a protein;

found in Staph (tested in S. aureus and S. epidermidis)

77
Q

What are the vanA/vanB markers, and where are they observed?

A

Markers of resistance to vancomycin; observed in enterococcus (tested in E. faecium and E. faecalis)

78
Q

What is an example of a carbapenemase gene?

A

KPC (Klebsiella pneumoniae carbapenemase)

79
Q

Most common ESBL marker

A

Cefotaxime isolated in Munich (CTX-M)

80
Q

Describe the CAMP test

A

Bacteria are cultured with Staph aureus. If they enlarge the beta-hemolysis area of S. aureus, the test is positive. Used to identify group B Strep (S. agalctiae).

81
Q

How can you distinguish between Neisseria species?

A

Maltose fermentation.

  • Yes => N. meningitides
  • No => N. gonorrhoeae
82
Q

How can you distinguish between Salmonella and Shigella species?

A

H2S production.

  • Yes=> Salmonella
  • No => Shigella

STEP 1 Microbiology (22 decks)

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