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Labs Medicine > Microbiology > Flashcards

Microbiology Flashcards

1
Q

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?

A

blastomyces dermatidis

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2
Q

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?

A

patient took antibiotics before sample was taken?

Organism that is difficult to culture?

Lab error?

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3
Q

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?

A

neisseria meningitides

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4
Q

58 y.o. male underwent biopsy of perirectal lesions. Histology revealed a granulomatous inflammatory reaction with caseating necrosis. What stain will confirm the diagnosis?

A

acid fast will reveal TB

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5
Q

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

A

direct detection (stains, antigen testing, molecular probes)

culture

serology

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6
Q

What are the general considerations when collecting a specimen for micro testing?

A
  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
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7
Q

What strategy gives the WORST type of sample? What are better?

A

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

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8
Q

How do you need to collect sterile body fluids (not CSF) if you know you’re going to need an anerobe culture?

A

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

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9
Q

Can you ever use a swabbed sample for culture?

A

Nope - never

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10
Q

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

A

3-4

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

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11
Q

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

A

3 on separate days

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12
Q

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

A

3 on alternate days

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13
Q

Gram positive cocci in changes is what?

A

strep

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14
Q

Which is catalase positive - staph or strep?

A

staph

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15
Q

Strep pyogenes is group __ strep

A

A

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16
Q

Strep pyogenes is __-hemolytic

A

beta

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17
Q

Strep pyogenes is bacitracin ____

A

susceptible

18
Q

Strep pyogenes has lancefield group ___ antigen

A

A

19
Q

Strep pneumoniae is ___-hemolytic

A

alpha

20
Q

strep pneumonia is opotochin ___ and bile ___.

A

optochin susceptible

bile soluble

21
Q

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.

A

Ignore - that low of a CFU/ml in an asymptmatic patient suggests it’s just a contaminant

22
Q

What is the 60-90 rule for antimicrobial susceptibility testing?

A

drug has a 90% change of success when organism is “susceptible”

a 60% changes of success when organism is “resistant”

23
Q

What is the Minimum inhibitory concentration (MIC)?

A

It’s the minimum inhibitory concentration of a drug that inhibits growth over a defined interval (usually 18-24 hrs)

24
Q

How does the beta-lactamase test work?

A

chromogenic cephalosporin substrate (nitrocefin) is hydrolyzed by the bacterial inoculum if they are b-lactamase positive, which will indicate pink on the test

25
Q

Positive beta-lactamase test suggests resistance to what antibiotics?

A 
pcn
amox
amp
pip
ticarcillin
26
Q

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?

A

carbapenemase

27
Q

Carbapenemases reside on what gene?

A

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

28
Q

What are the five different strategies for susceptibility testing?

A 
broth microdilution
agar dilution (single concentration per plate)
disk diffusion (more standardized)
antimicrobial gradient (Etest)
Automated instrument
29
Q

What lab test is typically used to identify microbe’s DNA or RNA in the host?

A

PCR amplification of a unique organism-specific sequence (qualitative more sensitive, quantitative more informative)

30
Q

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

A

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

31
Q

In what situations are host markers less helpful to make a diagnosis?

A

when the organism is ubiquitous (aspergillus)

when host is significantly immunocompromised (might not make antibodies anyways)

when host response is too non-specifict o be of diagnostic use (along with issue #1)

32
Q

The Polymerase chain reaction:

  1. Has been adapted for accurate quantification of viruses
  2. May yield false positive results when amplicons contaminate clinical samples
  3. Offers detection sensitivity which often, but not always exceeds that of culture
  4. all of the above
A

D

33
Q

The diagnosis of septicemia hsoul dbe considered in patients who are at increased risk of blood stream infection (often 2dary to local disease, such as UTI or PNA). All of the following are factors predisposing patients to septicemia except:

A. underlying disease that appear to compromis host defenses such as DM, lymphoma, etc.

B. Pts w/ a polymorphonuclear leukocyte count less than 1000/mm3

C. Pts with PMNs of 10K to 20K

D. Long term therapy with broad-spec ABx

A

C

34
Q

A 25 yo woman has a 4 yo son who is now recovering form GAS. Out of curiosity, the doc does a throat culture on mom, who is positive for GAS even though she doesn’t have a sore throat. The doc also does an ASO titer and anti DNAse B assay for her, both negative. At which point we would say that she has:

  1. asympomatic infection
    b. opportunistic infection
    c. is a carrier
    d. is immunosuppressed
A

c

35
Q

A 30 yo woman is admitted to hospital with a fever. Recently diagnosed with ALL and fnished chemo last week. Now essentially no WBCs. You perform 2 sets of blood cultures, sputum culture, urine culture and CXR. Only positive result is one blood culture with staph epi. This is a :

a. most likely cause of fever
b. most likely a contaminant
c. an indication she has meningitis
d. most likely an organism she got from a health care provider the last time she was in hospital

A

B

36
Q

45 yo woman admitted with acute chest pain. 2nd DOH, obvious it was an MI. Also develops acute diarrhea. Stool culture grows salmonella. This infection is:

a. hospital acquired
b. nosocomial
c. iatrogenic
d. community acquired

A

d (too early for hospital acquired)

37
Q

What are the most common causes of bacterial meningitis in newborns?

A

GBS
e coli
listeria

38
Q

What are the most common causes of bacterial meningitis in infants?

A

neisseria meningitidis
h. flu
strep pneumoniae

39
Q

What are the most common causes of bacterial meningitis in children?

A

n meningitidis

s pneumonia

40
Q

What are the most common causes of bacterial meningitis in adults?

A

s pneumonia
n meningitidis
myocbacteria

I think listeria in old people again?

Labs Medicine (27 decks)

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