B3.003 Prework 1 Culture Based Diagnostic Tests Flashcards

1
Q

Koch’s postulates

A
  1. microorganism present in every case of the infectious disease
  2. microorganism can be isolated in pure culture
  3. inoculation of pure culture into animals produces similar disease
  4. same species of microorganism recovered from diseased animal
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2
Q

difference between envelopes of gram - and + bacteria

A

gram +
-thick peptidoglycan layer
-variable capsule
-potential for pili and flagella within envelope
gram -
-thin peptidoglycan layer
-variable capsule
-cytoplasmic and outer membrane
-periplasmic space
-cytoplasmic membrane> periplasm> peptidoglycan > outer membrane > capsule
-potential for pili and flagella within envelope

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3
Q

what component of the gram - cell wall is responsible for shock

A

Lipopolysaccharide (LPS) endotoxin

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4
Q

gram stain technique

A
  1. heat fix
  2. crystal violet stains all cells purple
  3. iodine solution: mordant-complexes with CV
  4. ethanol-acetone: destain, gram + retain CV/iodine complex
  5. safranin: counterstain; stains all cells pink
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5
Q

mycobacteria gram stain results

A

gram positive
but lipids interfere with stain
use acid fast

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6
Q

spirochetes gram stain results

A

gram negative
too thin to resolve
use wright-giemsa stain

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7
Q

sputum specimen collection

A

lower respiratory tract infection

avoid saliva

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8
Q

urine specimen collection

A

urinary tract infection

minimize contact with normal flora

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9
Q

feces specimen collection

A

diarrhea
rapid transport
large number of cultures
no direct stains

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10
Q

tissue specimen collection

A

center and border of lesion

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11
Q

pus specimen collection

A

abscess
aspirate
avoid swab

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12
Q

blood culture specimen collection

A

bacteremia
avoid contamination
ensure enough volume is collected per draw, 2 draws per patient

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13
Q

swab specimen collection

A

upper respiratory tract infection
swab inflamed areas
avoid saliva STDs
not for anaerobes

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14
Q

where do natural bacterial populations exist

A

skin
respiratory tract (oral cavity, pharynx)
GI tract (primary large intestine)
urogenital tract

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15
Q

upper respiratory tract normal flora

A

staphylococcus
streptococcus
haemophilus
anaerobes

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16
Q

skin normal flora

A

staphylococcus
coryneform (diptheroids)
propionibacterium

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17
Q

GI tract normal flora

A
anaerobe
enterococcus
enterobacteriaceae
-Escherichia coli
-klebsiella
streptococcus
lactobacillus
candida
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18
Q

genital tract normal flora

A

lactobacillus

streptococcus

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19
Q

what characteristic of a sputum sample would indicate contamination?

A

> 10 epithelial cells per field

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20
Q

what feature of a sputum sample would indicate purulent infection?

A

presence of PMNs (polymononuclear cells)

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21
Q

growth media options

A

solid- agar

liquid - broth

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22
Q

enriched growth media

A

contains nutrients to support growth of a wide variety of organisms
blood agar, chocolate agar

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23
Q

selective growth media

A

inhibit growth of certain groups of organisms

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24
Q

differential growth media

A

distinguish organisms based on growth characteristics

25
obligate aerobe
requires oxygen for growth
26
facultative anaerobe
will grow in aerobic and anaerobic conditions
27
microaerophilic
grows best with low concentrations of oxygen
28
obligate anaerobe
oxygen is toxic
29
MacConkey Agar
selective: inhibits growth of gram + organisms differential: distinguished between ability to ferment lactose
30
viral culture
growth on mammalian cells not all viruses grow in viral culture replaced by molecular methods in most clinical labs
31
fungal culture
specialized media | incubation at lower temperature
32
mycobacterial culture
broth and solid media
33
alpha-hemolysis
green, incomplete lysis around colony
34
beta-hemolysis
clear zone around colony
35
gamma-hemolysis
no hemolysis
36
yellow pigment production
staphylococcus aureus
37
red/pink pigment production
serratia marcescens
38
blue green pigment production
pseudomonas aeruginosa
39
projections in colony
candida albicans
40
mucoid colony
klebsiella pneumoniae
41
swarming in colony
proteus vulgaris
42
catalase reaction
gas formation
43
coagulase reaction
precipitate formation
44
oxidase reaction
blue color | identifies pseudomonas, Neisseria, vibrio
45
methods of antimicrobial susceptibility testing (AST)
genotypic: PCR based detection of the genes associated with drug resistance phenotypic: tests ability of organisms to grow in the presence of drug
46
susceptible
isolate is inhibited by achievable concentrations of the antimicrobial agent
47
intermediate
response rate isolate may be lower than that for susceptible isolates
48
resistant
isolates are not inhibited by achievable concentrations of antimicrobial agent
49
limitations of AST
imprecise | does not take into effect host response, toxin production, biofilm formation
50
mecA gene
associated with methicillin resistance in s. aureus
51
vanA/B genes
associated with vancomycin resistance in enterococcus faecium
52
blaKPC gene
associated with carbapenem resistance
53
advantages of genotypic testing
fast very specific very sensitive
54
limitations of genotypic testing
expensive | single target
55
MIC
minimum inhibitory concentration | minimum concentration of a drug that will inhibit growth of the organism
56
methods of phenotypic testing
agar dilution broth microdilution disk diffusion strip
57
microbroth dilution
broth + increasing concentration of antibiotic in microtube or 96 well plate inoculate isolate into each well semi quantitiative
58
strip testing
``` paper strip with increasing concentration of drug inoculate plate with lawn of isolate place strip in center of plate read MIC at area of growth inhibition quantitative ```
59
disk diffusion test
paper disk w single concentration of antibiotic place on agar inoculated with testing bacteria measurement of the zones of growth inhibition does not give MIC