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EXAM 2 MLT124
MLT 124: MEDICAL MICRO PT I : EXAM II
| Question | Answer |
|---|---|
| What is the principle of Catalase test? | It is able to distinguish Staphylococci sp. from Streptococci sp. based on gas production. If a catalase enzyme is present, the bacteria can break down the hydrogen peroxide into oxygen and water, producing bubbles in positive results |
| True or False: The Oxidase test is utilized to differentiate between micrococcus species and staphylococcus species | False: Modified Oxidase testing uses an altered version of methyl phenylenediamine reagent to differentiate between the two species; the OG Oxidase testing determines presence of Gram negative bacilli |
| If a negative Modified Oxidase test shows no color change, what is expected of a positive result? | Blue/purple |
| The conversion of inactive fibrinogen to fibrin will result in (blank) for what kind of test? | clumping/agglutination; Coagulase testing |
| What is the difference between Bacitracin usage and Novobiocin usage? | Bacitracin is utilized to determine whether or not bacteria is of the Micrococcus sp. or Coag-neg staph. Novobiocin is used to determine S. saprophyticus presence in urine cultures |
| True or false: Any zone of inhibition for Novobiocin testing indicates a positive result for S. saprophyticus presence | False: Any zone of inhibition that is less than 16mm would indicate a negative result, proving S. saprophyticus presence. More than 16mm is positive for Coagulase-negative staph presence |
| If Bacitracin cannot inhibit bacterial cell wall synthesis, what type of bacteria are we dealing with? | Coagulase-negative Staphylococcus sp. |
| What testing separates Staph from Strept species? | Catalase |
| What is the order of testing we do, following a GPC stain? | Catalase, Coagulase - if both are negative, move on to Modified Oxidase/Bacitracin - negative/resistant, move onto Novobiocin testing |
| What additional testing can be done to confirm S. aureus presence? | MSA, VP, DNase, Staphyloslide |
| Describe the principle of MSA plate | Mannitol Salt Agar is a selective and differential media. The 7.5% concentration of salt deters bacteria that cannot survive in those conditions. Secondly, the agar's pH phenol will shift if the mannitol sugar is fermented, changing it from pink to yellow |
| Why might a DNase agar be performed? How will it look? | DNase is an exoenzyme produced by certain bacteria that increases its virulence, due to its ability to break down a host's cell DNA. Positive=visible clearing (glow) |
| What two reagents are utilized in the VP broth test? Describe the principle of the VP test. | Potassium hydroxide (KOH/Barrit's B) and Alpha napthol (Barrit's A). The production of acetoin changes the broth color to red on top. |
| PEA and Columbia CNA with Sheep Blood are media used to do what? | Separate Gram negatives from Gram positives within a mixed culture by inhibiting Gram negative growth |
| What substances are within Columbia CNA to differentiate based on hemolytic reactions? | Colistin and Nalidixic |
| True or false: Columbia CNA is a selective media that only allows for Gram positive growth and differentiates based on hemolytic activity | True |
| Due to the discontinued usage of methicillin against pathogenic bacteria, what drug is currently used to determine S. aureus susceptibility? How far must the zone of inhibition to prove S. aureus sensitivity? | Cefoxitin; 22mm< |
| What purpose does the presence of Oxacillin have within a MSA plate? | Only methicillin-resistant strains of bacteria will grow; this is additional information aside from salt tolerance and sugar fermentation ability |
| Why is chromogenic media becoming increasingly popular in the lab? What does it do? | It utilizes a color compound (chromogen) to assess an up-tick in enzymatic [phosphate] activity, which would cause a mauve-pink color to appear in MRSA colonies ( a result of hydrolysis) |
| Describe the principle of the PBP2 latex test? | Penicillin-bound protein 2 testing utilizes the mesA resistance gene to determine MRSA presence; visual agglutination will confirm MRSA bacteria because of the monoclonal coating within the latex reacting to the MRSA |
| While conducting Molecular testing, Gene probes can discover the (blank) gene, which is encoded into S. aureus to create methicillin resistance | mesA resistance gene |
| How does Beta-lactamase determine bacterial resistance? | It detects the penicillinase enzyme |
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