B3.003 Prework 1 Culture Based Diagnostic Tests

Question 1

Koch’s postulates

Answer 1

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

Question 2

difference between envelopes of gram - and + bacteria

Answer 2

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

Question 3

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

Answer 3

Lipopolysaccharide (LPS) endotoxin

Question 4

gram stain technique

Answer 4

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

Question 5

mycobacteria gram stain results

Answer 5

gram positive
but lipids interfere with stain
use acid fast

Question 6

spirochetes gram stain results

Answer 6

gram negative
too thin to resolve
use wright-giemsa stain

Question 7

sputum specimen collection

Answer 7

lower respiratory tract infection

avoid saliva

Question 8

urine specimen collection

Answer 8

urinary tract infection

minimize contact with normal flora

Question 9

feces specimen collection

Answer 9

diarrhea
rapid transport
large number of cultures
no direct stains

Question 10

tissue specimen collection

Answer 10

center and border of lesion

Question 11

pus specimen collection

Answer 11

abscess
aspirate
avoid swab

Question 12

blood culture specimen collection

Answer 12

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

Question 13

swab specimen collection

Answer 13

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

Question 14

where do natural bacterial populations exist

Answer 14

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

Question 15

upper respiratory tract normal flora

Answer 15

staphylococcus
streptococcus
haemophilus
anaerobes

Question 16

skin normal flora

Answer 16

staphylococcus
coryneform (diptheroids)
propionibacterium

Question 17

GI tract normal flora

Answer 17

anaerobe
enterococcus
enterobacteriaceae
-Escherichia coli
-klebsiella
streptococcus
lactobacillus
candida

Question 18

genital tract normal flora

Answer 18

lactobacillus

streptococcus

Question 19

what characteristic of a sputum sample would indicate contamination?

Answer 19

> 10 epithelial cells per field

Question 20

what feature of a sputum sample would indicate purulent infection?

Answer 20

presence of PMNs (polymononuclear cells)

Question 21

growth media options

Answer 21

solid- agar

liquid - broth

Question 22

enriched growth media

Answer 22

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

Question 23

selective growth media

Answer 23

inhibit growth of certain groups of organisms

Question 24

differential growth media

Answer 24

distinguish organisms based on growth characteristics

Question 25

obligate aerobe

Answer 25

requires oxygen for growth

Question 26

facultative anaerobe

Answer 26

will grow in aerobic and anaerobic conditions

Question 27

microaerophilic

Answer 27

grows best with low concentrations of oxygen

Question 28

obligate anaerobe

Answer 28

oxygen is toxic

Question 29

MacConkey Agar

Answer 29

selective: inhibits growth of gram + organisms differential: distinguished between ability to ferment lactose

Question 30

viral culture

Answer 30

growth on mammalian cells not all viruses grow in viral culture replaced by molecular methods in most clinical labs

Question 31

fungal culture

Answer 31

specialized media | incubation at lower temperature

Question 32

mycobacterial culture

Answer 32

broth and solid media

Question 33

alpha-hemolysis

Answer 33

green, incomplete lysis around colony

Question 34

beta-hemolysis

Answer 34

clear zone around colony

Question 35

gamma-hemolysis

Answer 35

no hemolysis

Question 36

yellow pigment production

Answer 36

staphylococcus aureus

Question 37

red/pink pigment production

Answer 37

serratia marcescens

Question 38

blue green pigment production

Answer 38

pseudomonas aeruginosa

Question 39

projections in colony

Answer 39

candida albicans

Question 40

mucoid colony

Answer 40

klebsiella pneumoniae

Question 41

swarming in colony

Answer 41

proteus vulgaris

Question 42

catalase reaction

Answer 42

gas formation

Question 43

coagulase reaction

Answer 43

precipitate formation

Question 44

oxidase reaction

Answer 44

blue color | identifies pseudomonas, Neisseria, vibrio

Question 45

methods of antimicrobial susceptibility testing (AST)

Answer 45

genotypic: PCR based detection of the genes associated with drug resistance phenotypic: tests ability of organisms to grow in the presence of drug

Question 46

susceptible

Answer 46

isolate is inhibited by achievable concentrations of the antimicrobial agent

Question 47

intermediate

Answer 47

response rate isolate may be lower than that for susceptible isolates

Question 48

resistant

Answer 48

isolates are not inhibited by achievable concentrations of antimicrobial agent

Question 49

limitations of AST

Answer 49

imprecise | does not take into effect host response, toxin production, biofilm formation

Question 50

mecA gene

Answer 50

associated with methicillin resistance in s. aureus

Question 51

vanA/B genes

Answer 51

associated with vancomycin resistance in enterococcus faecium

Question 52

blaKPC gene

Answer 52

associated with carbapenem resistance

Question 53

advantages of genotypic testing

Answer 53

fast very specific very sensitive

Question 54

limitations of genotypic testing

Answer 54

expensive | single target

Question 55

MIC

Answer 55

minimum inhibitory concentration | minimum concentration of a drug that will inhibit growth of the organism

Question 56

methods of phenotypic testing

Answer 56

agar dilution broth microdilution disk diffusion strip

Question 57

microbroth dilution

Answer 57

broth + increasing concentration of antibiotic in microtube or 96 well plate inoculate isolate into each well semi quantitiative

Question 58

strip testing

Answer 58

``` 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 ```

Question 59

disk diffusion test

Answer 59

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