Microbiology

Question 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?

Answer 1

blastomyces dermatidis

Question 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?

Answer 2

patient took antibiotics before sample was taken?

Organism that is difficult to culture?

Lab error?

Question 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?

Answer 3

neisseria meningitides

Question 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?

Answer 4

acid fast will reveal TB

Question 5

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

Answer 5

direct detection (stains, antigen testing, molecular probes)

culture

serology

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

Can you ever use a swabbed sample for culture?

Answer 9

Nope - never

Question 10

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

Answer 10

3-4

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

Question 11

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

Answer 11

3 on separate days

Question 12

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

Answer 12

3 on alternate days

Question 13

Gram positive cocci in changes is what?

Answer 13

strep

Question 14

Which is catalase positive - staph or strep?

Answer 14

staph

Question 15

Strep pyogenes is group __ strep

Answer 15

A

Question 16

Strep pyogenes is __-hemolytic

Answer 16

beta

Question 17

Strep pyogenes is bacitracin ____

Answer 17

susceptible

Question 18

Strep pyogenes has lancefield group ___ antigen

Answer 18

A

Question 19

Strep pneumoniae is ___-hemolytic

Answer 19

alpha

Question 20

strep pneumonia is opotochin ___ and bile ___.

Answer 20

optochin susceptible

bile soluble

Question 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.

Answer 21

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

Question 22

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

Answer 22

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

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

Question 23

What is the Minimum inhibitory concentration (MIC)?

Answer 23

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

Question 24

How does the beta-lactamase test work?

Answer 24

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

Question 25

Positive beta-lactamase test suggests resistance to what antibiotics?

Answer 25

``` pcn amox amp pip ticarcillin ```

Question 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?

Answer 26

carbapenemase

Question 27

Carbapenemases reside on what gene?

Answer 27

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

Question 28

What are the five different strategies for susceptibility testing?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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)

Question 32

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

Answer 32

D

Question 33

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

Answer 33

C

Question 34

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

Answer 34

c

Question 35

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

Answer 35

B

Question 36

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

Answer 36

d (too early for hospital acquired)

Question 37

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

Answer 37

GBS e coli listeria

Question 38

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

Answer 38

neisseria meningitidis h. flu strep pneumoniae

Question 39

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

Answer 39

n meningitidis | s pneumonia

Question 40

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

Answer 40

s pneumonia n meningitidis myocbacteria I think listeria in old people again?