Microbiology CSMLS prep || with 100% Errorless 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
2) nitrocefin test = turns from yellow to red = positive
3) acidimetric method = pH acidic = positive
what organism has group specific polysaccharide antigens on the cell wall that allow lancefield
grouping correct answers streptococcus
what organism smells like butterscotch? correct answers streptococcus anginosus
streptococcus pyogenes ID correct answers - gram pos cocci in chains
- catalase negative
- beta hemolytic
- nitrate negative
- bacitracin sensitive
- PYR positive
- Group A latex positive
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
2) nitrocefin test = turns from yellow to red = positive
3) acidimetric method = pH acidic = positive
what organism has group specific polysaccharide antigens on the cell wall that allow lancefield
grouping correct answers streptococcus
what organism smells like butterscotch? correct answers streptococcus anginosus
streptococcus pyogenes ID correct answers - gram pos cocci in chains
- catalase negative
- beta hemolytic
- nitrate negative
- bacitracin sensitive
- PYR positive
- Group A latex positive
