Lab Approaches to Infectious Diseases

Question 1

types of specimen collected for lab testing

Answer 1

1. sterile body fluid (blood, CSF, peritoneal/pleural/pericardial fluid, urine, eye/middle ear)
2. pus or sputum
3. stool
4. tissue biopsy (ex. lymph nodes)
5. lavage
6. swab of infected surface

Question 2

collection/transport methods for lab testing

Answer 2

-sterile cup (for stool/urine)
-blood culture bottles (has a vacuum in them)
-swabs
-viral transport media
-syringe

Question 3

laboratory accession and preparation

Answer 3

-specimens processed if needed (grinding of tissue or bone)
-specimens for molecular testing processed separately
-DIRECT MICROSCOPY performed on most specimens (gram stain, fungal smear, mycobacterial smears)
-cultures plated

Question 4

acid-fast stain

Answer 4

detect bacteria that have long-chain mycolic acid in the cell wall, which resist decolorization with acid

Question 5

dark-field microscopy

Answer 5

a special condenser is used that prevents transmitted light from directly illuminating the specimen
*used for spirochetes

Question 6

fluorescence microscopy

Answer 6

used to see a small number of organisms by using fluorochrome stain

Question 7

4 methods for bacterial identification in the lab

Answer 7

1. selective/chromogenic agar
2. biochemical analysis
3. MALDI-TOF
4. molecular

Question 8

MALDI-TOF

Answer 8

*rapid (get results in 1 hour)
*take a color, put it in matrix, a laser aerosolizes it; the further it goes down the column, the heavier it is
*computer tells you what organism is

Question 9

molecular testing

Answer 9

*several different tests, all based on identification of DNA or RNA
*PCR is an example of molecular testing

Question 10

PCR (polymerase chain reaction)

Answer 10

powerful technique for amplification and subsequent identification of DNA
1) denaturation into single strands
2) annealing of primers
3) extension of new DNA strnds
*requires Taq

Question 11

serology

Answer 11

-performed on serum usually
*can detect either ANTIGEN or IgM or IgG antibody
*ELISA is the most common form of serology
*useful for several viruses and bacteria

Question 12

minimal inhibitory concentration (MIC)

Answer 12

concentration of antimicrobial that INHIBITS growth
-commonly used by clinical lab

Question 13

minimal bacteriocidal concentration (MBC)

Answer 13

concentration that KILLS bacteria
-used clinically only in special circumstnaces

Question 14

resistant

Answer 14

somewhat arbitrary designation that implies that an antimicrobial will NOT inhibit bacterial growth at clinically achievable concentrations

Question 15

susceptible

Answer 15

somewhat arbitrary designation that implies that an antimicrobial WILL inhibit bacterial growth at clinically achievable concentrations

Question 16

breakpoint

Answer 16

the MIC that is used to designate between sensitive and resistant; arbitrarily set by a committee

Question 17

bacteriostatic

Answer 17

antibiotic that reversibly inhibits growth; host defenses usually complete killing and eradication

Question 18

bacteriocidal

Answer 18

antibiotic that kills microorganisms rapidly; probably important for difficult to treat infections