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Flashcards in Microbiology Deck (40)
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1

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?

blastomyces dermatidis

2

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?

Lab error?

3

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?

neisseria meningitides

4

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

5

What are the three general types of tests that can be used for microbiological diagnosis?

direct detection (stains, antigen testing, molecular probes)

culture

serology

6

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

7

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

8

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

9

Can you ever use a swabbed sample for culture?

Nope - never

10

How many blood culture sets are usually needed to R/O septicemia?

3-4

2 sets initially followed by a 3rd and 4th set at 4-6 h intervals

11

How my AFB cultures are needed to D/O a diagnosis for pulmonary TB?

3 on separate days

12

How many stool O&P specimens are needed to R/O a diagnosis of parasite diarrhea?

3 on alternate days

13

Gram positive cocci in changes is what?

strep

14

Which is catalase positive - staph or strep?

staph

15

Strep pyogenes is group __ strep

A

16

Strep pyogenes is __-hemolytic

beta

17

Strep pyogenes is bacitracin ____

susceptible

18

Strep pyogenes has lancefield group ___ antigen

A

19

Strep pneumoniae is ___-hemolytic

alpha

20

strep pneumonia is opotochin ___ and bile ___.

optochin susceptible
bile soluble

21

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

22

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"

23

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)

24

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

25

Positive beta-lactamase test suggests resistance to what antibiotics?

pcn
amox
amp
pip
ticarcillin

26

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?

carbapenemase

27

Carbapenemases reside on what gene?

blaKPC gene, which is located on a plasmid and can be transmitted

28

What are the five different strategies for susceptibility testing?

broth microdilution
agar dilution (single concentration per plate)
disk diffusion (more standardized)
antimicrobial gradient (Etest)
Automated instrument

29

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)

30

In what situations is it very heplfl to use a host marker of infection (antibody, etc.) instead of culture?

when the organism is very difficult to culture

when the presence of marker strongly suggests current infection (like HIV antibody)

test is more rapid than culture