if there is no zone of inhibition, what do you record? - Correct Answer 6mm because that accounts for
the disc
what causes sharp irregular zones around the sensitivity discs? - Correct Answer beta-lactam antibiotics
- indicates that beta-lactamase production by the bacteria and should be interpreted as resistant
susceptible vs intermediate vs resistant - Correct Answer - 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 Answer - 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 Answer - long term = frozen at -20C
- working supply in 4C
MRSA conditions - Correct Answer - 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 Answer - bovine hematin
- yeast extract
- NAD
- thymidine phosphorylase
E-test is beneficial for using it on - Correct Answer - anaerobes
- fastidious bacteria
E-test results interpretation: low MIC and high MIC - Correct Answer low MIC - sensitive
high MIC - resistant
Staphylococcus aureus characteristics - Correct Answer - 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 Answer - 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 Answer - 6ug oxacillin
- 4% NaCl
- any growth on plate = resistant
,slide coagulase vs tube coagulase - Correct Answer - slide = bound coagulase
- tube = free coagulase
false negative coagulase tests are commonly from - Correct Answer weak bacterial suspensions
gold standard of staph aureus is - Correct Answer positive tube coagulase
what is found on the cell wall of S. aureus but not other staph species? - Correct Answer Protein A and
clumping factor = used in latex reagent methods
thermostable nuclease test is used for - Correct Answer ID of staph aureus
- food microbiology investigations of food poisoning
staphylococcus saprophyticus ID - Correct Answer - bright white opaque colonies
- catalase positive
- nitrate positive
- novobiocin resistant
- common UTI
what virulence factors does staphylococcus aureus have? - Correct Answer - leucocidin
- hyaluronidase
- staphylokinase (clots)
- hemolysins
_______ is the most common cause of skin, soft tissue and post traumatic infections - Correct Answer S.
aureus
, three diseases caused by S. aureus exotoxins - Correct Answer 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 Answer - penicillin G
- beta-lactamase (oxacillin and methicillin)
drug of choice for MRSA - Correct Answer vancomycin
catalase test: reagent and purpose - Correct Answer - 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 Answer - light and heat
- store in amber bottle in fridge
- QC done daily
false positives for catalase - Correct Answer - platinum wires
- picking up some of the BAP agar
false negatives for catalase - Correct Answer - older colonies
- breakdown of hydrogen peroxide
QC organisms for catalase - Correct Answer - positive = staph
the disc
what causes sharp irregular zones around the sensitivity discs? - Correct Answer beta-lactam antibiotics
- indicates that beta-lactamase production by the bacteria and should be interpreted as resistant
susceptible vs intermediate vs resistant - Correct Answer - 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 Answer - 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 Answer - long term = frozen at -20C
- working supply in 4C
MRSA conditions - Correct Answer - 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 Answer - bovine hematin
- yeast extract
- NAD
- thymidine phosphorylase
E-test is beneficial for using it on - Correct Answer - anaerobes
- fastidious bacteria
E-test results interpretation: low MIC and high MIC - Correct Answer low MIC - sensitive
high MIC - resistant
Staphylococcus aureus characteristics - Correct Answer - 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 Answer - 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 Answer - 6ug oxacillin
- 4% NaCl
- any growth on plate = resistant
,slide coagulase vs tube coagulase - Correct Answer - slide = bound coagulase
- tube = free coagulase
false negative coagulase tests are commonly from - Correct Answer weak bacterial suspensions
gold standard of staph aureus is - Correct Answer positive tube coagulase
what is found on the cell wall of S. aureus but not other staph species? - Correct Answer Protein A and
clumping factor = used in latex reagent methods
thermostable nuclease test is used for - Correct Answer ID of staph aureus
- food microbiology investigations of food poisoning
staphylococcus saprophyticus ID - Correct Answer - bright white opaque colonies
- catalase positive
- nitrate positive
- novobiocin resistant
- common UTI
what virulence factors does staphylococcus aureus have? - Correct Answer - leucocidin
- hyaluronidase
- staphylokinase (clots)
- hemolysins
_______ is the most common cause of skin, soft tissue and post traumatic infections - Correct Answer S.
aureus
, three diseases caused by S. aureus exotoxins - Correct Answer 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 Answer - penicillin G
- beta-lactamase (oxacillin and methicillin)
drug of choice for MRSA - Correct Answer vancomycin
catalase test: reagent and purpose - Correct Answer - 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 Answer - light and heat
- store in amber bottle in fridge
- QC done daily
false positives for catalase - Correct Answer - platinum wires
- picking up some of the BAP agar
false negatives for catalase - Correct Answer - older colonies
- breakdown of hydrogen peroxide
QC organisms for catalase - Correct Answer - positive = staph
