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clinical microbio lab methods Flashcards

1
Q

aerobic likes what atmosphere conditions

A

oxygen rich

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2
Q

anaerobic likes what atmosphere conditions

A

oxygen deplete

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3
Q

microaerophilic likes what atmosphere conditions

A

low oxygen

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4
Q

describe what an obligate/strict aerobe does

A

bacteria gathers at the top of the test tube to absorb maximal amount of oxygen

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5
Q

describe what a microaerophile does

A

gathers at the upper part of the test tube, not at the top (requires oxygen, but at a low concentration)

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6
Q

describe what a facultative anaerobe does

A

gathers mostly at the top, since aerobic respiration is most beneficial, but as lack of oxygen does not hurt them, they can be found all along the test tube

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7
Q

describe what an aerotolerant does

A

bacteria are not affected by oxygen and they are evenly spread along the test tube

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8
Q

describe what an obligate (strict) anaerobe does

A

bacteria gather at the bottom to avoid oxygen

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9
Q

what are the steps of the gram stain

A
  1. apply crystal violet (purple dye)
  2. apply iodine (mordant)
  3. alcohol wash (decolorization)
  4. apply safranin (counterstain)
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10
Q

a pink stain means gram ___

A

negative

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11
Q

a purple stain means gram ____

A

positive

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12
Q

no/minimal stain means ____

A

atypical

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13
Q

cocci means ___

A

sphere

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14
Q

bacilli means ___

A

rod

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15
Q

why is gram stain important

A

typically first result provided by lab

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16
Q

what are common configurations that gram stains reveal

A

pairs, chains, clusters

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17
Q

what are common morphologies that gram stains reveal

A

cocci, bacilli

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18
Q

cocci in clusters are ____

A

staphylococcus

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19
Q

cocci in chains are ____

A

streptococcus

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20
Q

coagulase positive staph is ____

A

staph aureus

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21
Q

coagulase negative staph is _____

A

staph epidermidis, staph. saprophyticus, staph. lugdunensis

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22
Q

group A strep is ____

A

pyogenes

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23
Q

group B strep is ____

A

agalactiae

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24
Q

strep pneumoniae may appear in ____

A

pairs (diplococci)

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25
Q

what pathogens are rods (bacilli)

A

bacillus cereus, corynebacterium, listeria monocytogenes, clostridium

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26
Q

cocci in pairs and chains are ____

A

enterococcus (E. faecalis, E. faecium)

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27
Q

growth characteristics on visual inspection of culture plates: staph. aureus?

A

golden colonies grow on the agar

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28
Q

______ are extra-cellular bacterial proteins that degrade red blood cell lipid membranes

A

hemolysins

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29
Q

what pathogens have alpha hemolysis (green agar, partial hemolysis)

A

strep pneumoniae, viridans strep.

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30
Q

what pathogens have beta hemolysis (clear zone of hemolyzed RBCs around bacteria)

A

strep pyogenes, strep agalactiae, staph aureus

31
Q

what pathogen has gamma hemolysis (no hemolysis)

A

enterococcus

32
Q

what does the catalase test differentiate

A

streptococci and staphylococci

33
Q

streptococci is catalase _____

34
Q

staphylococci is catalase ____

35
Q

what does the coagulase test differentiate

A

staphylococcus aureus from other staphylococci

36
Q

staphylococcus aureus is coagulase ____

37
Q

staph. epidermidis is coagulase ____

38
Q

what are the methods for streptococci differentiation for presumptive ID?

A
  1. catalase negative
  2. hemolysis patterns on blood agar
  3. agglutination
  4. resistance: optochin disk test, bile solubility
39
Q

what determines the lancefield groups (a, b, c, d, f, g)

A

agglutination: the beta-hemolytic group is further differentiated by antibody-antigen agglutination reactions

40
Q

what are some biochemical differentiation tests for gram negatives?

A

lactose fermentation, indole test, enzyme expression

41
Q

describe lactose fermentation test?

A

acid production and color change of the growth medium can indicate which sugars are used by the organism

42
Q

describe indole test?

A

product of tryptophan metabolism

43
Q

describe enzyme expression tests?

A

urease, oxidase

44
Q

what are biological differentiation tests for gram negatives?

45
Q

what are the commonly encountered gram (-) bacilli lactose fermenters in the HS?

A

citrobacter freundii, escherichia coli, klebsiella aerogenes, enterobacter cloacae, klebsiella pneumoniae, klebsiella oxytoca, serratia marcescens

46
Q

what are the commonly encountered gram (-) bacilli non-lactose fermenters in the HS?

A

pseudomonas aeruginosa, stenotrophomonas maltophilia, proteus mirabilis and vulgaris, providencia stuartii

47
Q

proteus is urease __

48
Q

pseudomonas is oxidase _

49
Q

what are the commonly encountered gram negative cocci in the HS?

A

moraxella catarrhalis, neisseria meningitidis, neisseria gonorrhea, acinetobacter baumanii, haemophilus influenzae

50
Q

what are the common anaerobes in the HS

A

actinomyces, bacteroides, clostridial

51
Q

what are the common atypicals in the HS

A

legionella pneumophilia, chlamydophila pneumoniae, mycoplasma pneumoniae

52
Q

what bacteria are acid-fast (do not take up gram stain)

A

mycobacterium tuberculosis, non-tubercular mycobacteria

53
Q

what are rapid tests??

A

non-culture based: no culture growth is required

54
Q

advantages of rapid tests

A

genus and species identification in hours versus days, may identify presence of resistance gene determinants, reduce time to effective therapy

55
Q

what are limitations of rapid tests

A

typically no susceptibility data, and no culture prepared to conduct susceptibility testing. only some resistance gene determinants available for detection. not uniformly adopted across health systems due to cost

56
Q

bacterial resistance genes can be ____ or _____

A

inherent to the organism (chromosome mediated) or acquired (transferred on plasmids)

57
Q

what resistance genes are detectable by GenMark Eplex

A

mecA, mecC for MRSA
vanA, vanC for VRE

58
Q

what are 3 testing methods for antibacterial susceptibility

A

disk diffusion (kirby bauer), broth dilution, e-test

59
Q

kirby bauer (disk diffusion) determines _____

A

zone diameter of bacterial growth inhibiton

60
Q

broth-dilution and E-test determine ___

61
Q

MIC and zone of inhibition are referenced to a set of standardized interpretations known as ___

A

breakpoints

62
Q

what is the MIC

A

the lowest concentration of an antibiotic that inhibits visible growth of a microorganism

63
Q

the ____ the MIC on an E-test, the more potent the antibiotic

64
Q

the ____ the zone of inhibiton on a kirby-bauer test, the more potent the antibiotic

65
Q

who provides the standards for interpreting susceptibility testing results in the united states

A

CLSI- clinical laboratory standards institute

66
Q

what are some rapid susceptibility tests for detection of resistance genes

A

molecular: DNA FISH (fluorescence in situ hybridization), PCR (mecA/mecC, VanA/VanB, CTXM)
rapid phenotype
others: PBP2a, lateral flow, agglutination

67
Q

what kind of bacteria are difficult to grow and test susceptibility?

A

anaerobes due to environmental growth requirements

68
Q

what is a full susceptibility panel

A

all results are released

69
Q

what is a scaffolded susceptibility panel

A

results are released for broad/novel spectrum agents only if the organism is resistant to multiple drug classes

70
Q

what is a selective susceptibility panel

A

results are released for only agents not expected to develop resistance during treatment

71
Q

types of antibiograms

A

by region, by institution, by site of infection, for a specified period of time

72
Q

who requires antibiograms

A

hospitals and LTCFs

73
Q

what is the minimum number of isolates required for antibiogram reliability

ID2 (13 decks)

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