Flashcards in Microbiology Deck (40)
13 y.o. male with worsening respiratory symptoms despite weeks of antimicrobial therapy for bacterial pneumonia was transferred to UIHC and underwent bronchoscopy. Calcaluor white stain shows broad based buddying yeast forms indicative of what?
CSF from an 18 year old female with symptoms of meningitis was submitted to the Microbiology lab for testing. The gram stain revealed organisms but the culture was “no growth”. What are possible explanations?
patient took antibiotics before sample was taken?
Organism that is difficult to culture?
For the patient in the previous question, the gram stain revealed gram negative diplococci in pairs; an organism that can be grown out on chocolate agar. What's the diagnosis?
58 y.o. male underwent biopsy of perirectal lesions. Histology revealed a granulomatous inflammatory reaction with caseating necrosis. What stain will confirm the diagnosis?
acid fast will reveal TB
What are the three general types of tests that can be used for microbiological diagnosis?
direct detection (stains, antigen testing, molecular probes)
What are the general considerations when collecting a specimen for micro testing?
1. ideally get specimen before ABx
2. avoid contamination with normal flora
3. collect an adequate volume
4. use appropriate transport device
5. get to lab ASAP at specified temp
What strategy gives the WORST type of sample? What are better?
swabs - they pick up etraneous microbes, don't hold much and it's hard to get the bacteria off the fibers and onto the media
tissue samples and aspirates are much better
How do you need to collect sterile body fluids (not CSF) if you know you're going to need an anerobe culture?
use anaerobic vial for transport
cleanse the rubber septum of the contained with 70% alcohol and allow it to dry for 1 min before inoculating
disinfect the overlying skin with iodine or chlorhexidine
Can you ever use a swabbed sample for culture?
Nope - never
How many blood culture sets are usually needed to R/O septicemia?
2 sets initially followed by a 3rd and 4th set at 4-6 h intervals
How my AFB cultures are needed to D/O a diagnosis for pulmonary TB?
3 on separate days
How many stool O&P specimens are needed to R/O a diagnosis of parasite diarrhea?
3 on alternate days
Gram positive cocci in changes is what?
Which is catalase positive - staph or strep?
Strep pyogenes is group __ strep
Strep pyogenes is __-hemolytic
Strep pyogenes is bacitracin ____
Strep pyogenes has lancefield group ___ antigen
Strep pneumoniae is ___-hemolytic
strep pneumonia is opotochin ___ and bile ___.
A urine culture accidentally is ordered on a 28 yo asymptomatic female patient. Results come back as 5,000 CFU/ml of E. coli. What should you do with these results.
Ignore - that low of a CFU/ml in an asymptmatic patient suggests it's just a contaminant
What is the 60-90 rule for antimicrobial susceptibility testing?
drug has a 90% change of success when organism is "susceptible"
a 60% changes of success when organism is "resistant"
What is the Minimum inhibitory concentration (MIC)?
It's the minimum inhibitory concentration of a drug that inhibits growth over a defined interval (usually 18-24 hrs)
How does the beta-lactamase test work?
chromogenic cephalosporin substrate (nitrocefin) is hydrolyzed by the bacterial inoculum if they are b-lactamase positive, which will indicate pink on the test
Positive beta-lactamase test suggests resistance to what antibiotics?
63 yo pt becomes febrile while hospitalized for treatment of CLL. Aerobic and anaerobic blood cultures are collected and the automated instrument confirms that it is klepsiella pneumoniae and confirms the susceptibility profile with resistant to meropenem. This means the bacteria likely has what?
Carbapenemases reside on what gene?
blaKPC gene, which is located on a plasmid and can be transmitted
What are the five different strategies for susceptibility testing?
agar dilution (single concentration per plate)
disk diffusion (more standardized)
antimicrobial gradient (Etest)
What lab test is typically used to identify microbe's DNA or RNA in the host?
PCR amplification of a unique organism-specific sequence (qualitative more sensitive, quantitative more informative)