Fundamentals of Clinical Micro

Question 1

How many steps are involved in specimen processing?

which test happens twice?

Answer 1

nine steps!

There are two gram stains done, 1) direct GS of the primary sample
2) gram stain of colonies that grow

Question 2

When are swabs okay to use for specimen collection?

Answer 2

• for superficial skin lesions
• the throat
• nasopharyngeal sites

BUT, pieces of tissue or aspirates are superior to swabs!

Question 3

What kind of specimen may be injected into no additive tubes?

Answer 3

ones not cultured fro anaerobes

Question 4

What allows lab staff to determine the prominent organism on a plate?

Answer 4

they look for one colony type that makes up >50% of everything, if they cannot say that, then need a better sample (other than sputum)

Question 5

What makes a plate culture a clinically significant find?

Answer 5

• very few colony types, with one isolate in great abundance.
• growth to the bottom of the plate
• if there is growth w/ a smaller inoculum (1x10^5)

Question 6

The level of ID is determined by the potential clinical significance, which is based on: (5)

Answer 6

• site
• potential pathogen vs. normal flora
• quantity
• mixed vs. pure culture
• correlation w/ gram stain

Question 7

MALDI-TOF

Answer 7

mass spec method that is inexpensive and extremely rapid.

• any organisms w/ a unique protein mass spectrum can theoretically be identified
• fingerprint mass!

Question 8

What does antimicrobial susceptibility testing tell us?

Answer 8

• most narrow spectrum
• least expensive agent
• based on MIC of a drug

**must remember the 90-60 rule, 90% success when susceptible, 60% success when resistant!

Question 9

Carbapenemases

Answer 9

-organisms that have resistance genes to carbapenems on plasmids
ex)K. pneumoniae carbapenemase (KPC)
or Carbapenem resistant enterobacteriaceae (CRE)