MICROBIOLOGY CSMLS EXAM PREP
QUESTIONS & ANSWERS
if there is no zone of inhibition, what do you record? - Correct Answers -6mm because
that accounts for the disc
what causes sharp irregular zones around the sensitivity discs? - Correct Answers -
beta-lactam antibiotics
- indicates that beta-lactamase production by the bacteria and should be interpreted as
resistant
susceptible vs intermediate vs resistant - Correct Answers -- susceptible = susceptible
to action of the antimicrobials and is stopped or killed by it
- intermediate = used for certain drug combinations that are difficult to test or produce
results of certainty
- resistant = resistant to the action of antimicrobial and keeps growing in its presence
QC for susceptibility tests - Correct Answers -- each time new discs or panels are
received
- each time tests are performed (once a week)
- organisms are staph aureus, E.coli, pseudo, enterococcus
how should antimicrobial discs be stored? - Correct Answers -- long term = frozen at -
20C
- working supply in 4C
MRSA conditions - Correct Answers -- addition of NaCl
- 30-35C (lower temp is better)
- displays trailing on disc diffusion methods
- healthcare workers are screened for it
- use oxacillin screen test
Haemophilus test medium (HTM) is supplemented with - Correct Answers -- bovine
hematin
- yeast extract
- NAD
,- thymidine phosphorylase
E-test is beneficial for using it on - Correct Answers -- anaerobes
- fastidious bacteria
E-test results interpretation: low MIC and high MIC - Correct Answers -low MIC -
sensitive
high MIC - resistant
Staphylococcus aureus characteristics - Correct Answers -- double zone of beta
hemolysis
- creamy yellow color from lipochrome @48H
- ferments mannitol (yellow)
- catalase positive
- nitrate positive
- slide or TUBE coagulase positive
MSA media (mannitol salt agar) - Correct Answers -- 7.5% NaCl
- differential = mannitol and phenol red
- if it ferments mannitol it will be yellow, if it does not then it will be red
- staph aureus ferments (yellow)
MRSA oxacillin screen test - Correct Answers -- 6ug oxacillin
- 4% NaCl
- any growth on plate = resistant
slide coagulase vs tube coagulase - Correct Answers -- slide = bound coagulase
- tube = free coagulase
false negative coagulase tests are commonly from - Correct Answers -weak bacterial
suspensions
gold standard of staph aureus is - Correct Answers -positive tube coagulase
what is found on the cell wall of S. aureus but not other staph species? - Correct
Answers -Protein A and clumping factor = used in latex reagent methods
thermostable nuclease test is used for - Correct Answers -ID of staph aureus
- food microbiology investigations of food poisoning
staphylococcus saprophyticus ID - Correct Answers -- bright white opaque colonies
- catalase positive
- nitrate positive
- novobiocin resistant
,- common UTI
what virulence factors does staphylococcus aureus have? - Correct Answers --
leucocidin
- hyaluronidase
- staphylokinase (clots)
- hemolysins
_______ is the most common cause of skin, soft tissue and post traumatic infections -
Correct Answers -S. aureus
three diseases caused by S. aureus exotoxins - Correct Answers -1) food poisoning -
heat stable enterotoxin (fast)
2) toxic shock syndrome - tampons
3) scalded skin syndrome - rash & desquamation of skin
what antibiotics can staphylococcus have? - Correct Answers -- penicillin G
- beta-lactamase (oxacillin and methicillin)
drug of choice for MRSA - Correct Answers -vancomycin
catalase test: reagent and purpose - Correct Answers -- 3% hydrogen peroxide
- detects catalase enzyme by breaking the hydrogen peroxide down into water and
oxygen
- differentiates staph from strep
- also shows/IDs anaerobes
what can cause breakdown of catalase reagent (hydrogen peroxide)? - Correct Answers
-- light and heat
- store in amber bottle in fridge
- QC done daily
false positives for catalase - Correct Answers -- platinum wires
- picking up some of the BAP agar
false negatives for catalase - Correct Answers -- older colonies
- breakdown of hydrogen peroxide
QC organisms for catalase - Correct Answers -- positive = staph
- negative = strep
nitrate reduction test - Correct Answers -- durham tube collects gas (positive)
, - reagents A and B are added, if red = positive
- zinc dust is added and if colourless = positive
- used as the staph genus test
what are reagents A and B in nitrate test? - Correct Answers -Reagent A - sulfanilic acid
in acetic acid
Reagent B - alpha naphthylamine in acetic acid
reagent for coagulase is - Correct Answers -rabbit plasma
false positive coagulase tests - Correct Answers -- citrate anticoagulant = false clotting
- autoagglutination
-
false negative coagulase tests - Correct Answers -- weak bacterial suspension
- incubation over 35C
- frequent and excess agitation
- if serum is used = no fibrinogen = no clot
QC organisms for coagulase test - Correct Answers -positive = staph aureus
negative = staph epidermidis
DNase test: purpose and positive organisms - Correct Answers -- purpose is to detect
enzyme that depolymerizes (unwinds) DNA and convert it into oligonucleotides
- staph aureus
- Moraxella
- serratia
- xanthomonas maltophilia
oligonucleotides can be detected in the DNase test by - Correct Answers -- hydrochloric
acid (clearing = positive, cloudy = negative)
- methyl green (green = negative, colourless = positive)
- toluidine blue (blue = negative, pink = positive)
QC organisms for DNase test - Correct Answers -positive = staph aureus or serratia
negative = staph epidermidis or E.coli
Beta-lactamase different methods of detection - Correct Answers -1) iodometric method
= penicillin, starch and iodine. Loss of purple colour = positive
QUESTIONS & ANSWERS
if there is no zone of inhibition, what do you record? - Correct Answers -6mm because
that accounts for the disc
what causes sharp irregular zones around the sensitivity discs? - Correct Answers -
beta-lactam antibiotics
- indicates that beta-lactamase production by the bacteria and should be interpreted as
resistant
susceptible vs intermediate vs resistant - Correct Answers -- susceptible = susceptible
to action of the antimicrobials and is stopped or killed by it
- intermediate = used for certain drug combinations that are difficult to test or produce
results of certainty
- resistant = resistant to the action of antimicrobial and keeps growing in its presence
QC for susceptibility tests - Correct Answers -- each time new discs or panels are
received
- each time tests are performed (once a week)
- organisms are staph aureus, E.coli, pseudo, enterococcus
how should antimicrobial discs be stored? - Correct Answers -- long term = frozen at -
20C
- working supply in 4C
MRSA conditions - Correct Answers -- addition of NaCl
- 30-35C (lower temp is better)
- displays trailing on disc diffusion methods
- healthcare workers are screened for it
- use oxacillin screen test
Haemophilus test medium (HTM) is supplemented with - Correct Answers -- bovine
hematin
- yeast extract
- NAD
,- thymidine phosphorylase
E-test is beneficial for using it on - Correct Answers -- anaerobes
- fastidious bacteria
E-test results interpretation: low MIC and high MIC - Correct Answers -low MIC -
sensitive
high MIC - resistant
Staphylococcus aureus characteristics - Correct Answers -- double zone of beta
hemolysis
- creamy yellow color from lipochrome @48H
- ferments mannitol (yellow)
- catalase positive
- nitrate positive
- slide or TUBE coagulase positive
MSA media (mannitol salt agar) - Correct Answers -- 7.5% NaCl
- differential = mannitol and phenol red
- if it ferments mannitol it will be yellow, if it does not then it will be red
- staph aureus ferments (yellow)
MRSA oxacillin screen test - Correct Answers -- 6ug oxacillin
- 4% NaCl
- any growth on plate = resistant
slide coagulase vs tube coagulase - Correct Answers -- slide = bound coagulase
- tube = free coagulase
false negative coagulase tests are commonly from - Correct Answers -weak bacterial
suspensions
gold standard of staph aureus is - Correct Answers -positive tube coagulase
what is found on the cell wall of S. aureus but not other staph species? - Correct
Answers -Protein A and clumping factor = used in latex reagent methods
thermostable nuclease test is used for - Correct Answers -ID of staph aureus
- food microbiology investigations of food poisoning
staphylococcus saprophyticus ID - Correct Answers -- bright white opaque colonies
- catalase positive
- nitrate positive
- novobiocin resistant
,- common UTI
what virulence factors does staphylococcus aureus have? - Correct Answers --
leucocidin
- hyaluronidase
- staphylokinase (clots)
- hemolysins
_______ is the most common cause of skin, soft tissue and post traumatic infections -
Correct Answers -S. aureus
three diseases caused by S. aureus exotoxins - Correct Answers -1) food poisoning -
heat stable enterotoxin (fast)
2) toxic shock syndrome - tampons
3) scalded skin syndrome - rash & desquamation of skin
what antibiotics can staphylococcus have? - Correct Answers -- penicillin G
- beta-lactamase (oxacillin and methicillin)
drug of choice for MRSA - Correct Answers -vancomycin
catalase test: reagent and purpose - Correct Answers -- 3% hydrogen peroxide
- detects catalase enzyme by breaking the hydrogen peroxide down into water and
oxygen
- differentiates staph from strep
- also shows/IDs anaerobes
what can cause breakdown of catalase reagent (hydrogen peroxide)? - Correct Answers
-- light and heat
- store in amber bottle in fridge
- QC done daily
false positives for catalase - Correct Answers -- platinum wires
- picking up some of the BAP agar
false negatives for catalase - Correct Answers -- older colonies
- breakdown of hydrogen peroxide
QC organisms for catalase - Correct Answers -- positive = staph
- negative = strep
nitrate reduction test - Correct Answers -- durham tube collects gas (positive)
, - reagents A and B are added, if red = positive
- zinc dust is added and if colourless = positive
- used as the staph genus test
what are reagents A and B in nitrate test? - Correct Answers -Reagent A - sulfanilic acid
in acetic acid
Reagent B - alpha naphthylamine in acetic acid
reagent for coagulase is - Correct Answers -rabbit plasma
false positive coagulase tests - Correct Answers -- citrate anticoagulant = false clotting
- autoagglutination
-
false negative coagulase tests - Correct Answers -- weak bacterial suspension
- incubation over 35C
- frequent and excess agitation
- if serum is used = no fibrinogen = no clot
QC organisms for coagulase test - Correct Answers -positive = staph aureus
negative = staph epidermidis
DNase test: purpose and positive organisms - Correct Answers -- purpose is to detect
enzyme that depolymerizes (unwinds) DNA and convert it into oligonucleotides
- staph aureus
- Moraxella
- serratia
- xanthomonas maltophilia
oligonucleotides can be detected in the DNase test by - Correct Answers -- hydrochloric
acid (clearing = positive, cloudy = negative)
- methyl green (green = negative, colourless = positive)
- toluidine blue (blue = negative, pink = positive)
QC organisms for DNase test - Correct Answers -positive = staph aureus or serratia
negative = staph epidermidis or E.coli
Beta-lactamase different methods of detection - Correct Answers -1) iodometric method
= penicillin, starch and iodine. Loss of purple colour = positive
