Fundamentals of clinical microbiology

Question 1

what is the one organism you don’t want to miss on a respiratory culture?

Answer 1

strep pneumo - major pathogen, causes a lot of disease, especially in elderly.

Question 2

when is it okay to use swabs (normally they suck)

Answer 2

• superficial skin lesions
• throat
• nasopharyngeal sites

Question 3

what does strep pneumo look like on blood agar?

Answer 3

• a-hemolytic

- abundant growth.

Question 4

what is the new paradigm for ID of bacterial organisms?

Answer 4

MALDI-TOF (type of mass spec testing)

-costs under a dollar and takes an hour.

Question 5

90-60 rule for antibiotic susceptibility testing.

Answer 5

if organism is “susceptible”, that antibiotic has a 90% (or higher) chance of success

if organism is “resistant”, that antibiotic has a 60% (or lower) chance of success

Question 6

main mechanism of antibiotic susceptibility testing.

Answer 6

commercial AST systems

ETest as a backup

Question 7

factors that affect which drugs show up on the antibiotic susceptibility test report.

Answer 7

• formulary (cost)

- location of infection

Question 8

classic case of strep pharyngitis. pre-test probability is 80%. Negative rapid test moves post test probability to 65%. Treat?

Answer 8

Yes - probably still worth it due to complications of strep infections

Question 9

On antibiotic susceptibility testing, you see resistance to a a carbapenam (meropenem)
along with a
3rd gen cephalosporin (ceftriaxone).

What is your conclusion?

Answer 9

Oh Shit.

-You probably have a carbapenemase producing strain of Klebsiella Pneumoniae on your hands

Question 10

which strain produces carbapenemase?

Answer 10

Klebsiella Pneumoniae was the first one. Now the plasmid has been transferred to other enterobacteriaceae.