Microbiology - Antib Sens Testing

Front 1

What bacteria uses altered permeability as its mechanism of resistance?

Back 1

Pseudomonas, resistance to aminoglycosides

Front 2

What bacteria uses altered receptors or binding proteins as a mechanism of resistance?

Back 2

S. pna
MRSA

Front 3

To determine antibiotic resistance, one must have a pure culture in log-phase growth, which is usually what?

Back 3

18-24 hours old

Front 4

What is 0.5 McFarland?

Back 4

Barium sulfate standard equal to the turbidity of 10^8 bacteria/ml

Front 5

How many days of QC are needed to implement a new method?

Back 5

20 consecutive days, using ATCC (known) strains
Then weekly QC on all lots

Front 6

What to do if the weekly QC is OUT OF CONTROL!

Back 6

- Inform supervisor
- Repeat test
- If repeat is normal, move on
- If repeat not ok, investigate and repeat x 5 (all must be ok)

Front 7

What is the preferred agar for a Kirby Bauer test and why?

Plate diameter and depth?

Back 7

Mueller Hinton agar

Specially balanced with the proper amounts of Ca++, Mg++

(Too much concentration can give FALSE RESISTANCES TO AMINOGLYCOSIDES)

150mm diameter, 4mm depth

Front 8

Can you compare zones of inhibition between antibiotics using a Kirby Bauer?

Back 8

NO!! Never compare zone sizes. CLSI charts tell sensitive/resistant/intermediate based on unique zone sizes for each antibiotic

Front 9

What is the difference between MIC and MBC?

Back 9

MIC: lowest concentration of antibiotic that inhibits growth

MBC: lowest concentration of antibiotic that kills 99.9% of original inoculum (subculture the "no growth" from MIC)

Front 10

What is "Antibiotic tolerance"?

Back 10

(MBC / MIC) >= 32

BAD!

Can't kill the organism but can inhibit it

Front 11

When would we use e test over KB?

Back 11

E tests are good for fastidious organisms

Also, e test directly gives MIC

Front 12

What % of haemophilus is resistant to ampicillin, via disk test for B-lactamase detection?

Back 12

28%

Front 13

What is the primary mechanism for PCN resistance in B frag?

Back 13

B lactamase. Test with disk test for B lactamase

Front 14

What is the chromogenic cephalosporin used for the disk test for B lactamase detection?

Back 14

Nitrocefin. turns from yellow to red in the presence of B lactamase

Front 15

What is the mechanism of resistance in MRSA?

Back 15

mecA gene encodes PBPs (Pcn binding proteins)

Front 16

What drug do we test in the lab for MRSA?

Back 16

Oxacillin (actually now we mostly use cefoxitin for increased sensitivity)

Front 17

How to increase sensitivity of MRSA detection?

Back 17

Adding 4% NaCl to the agar
Using cefoxitin instead of oxacillin

Front 18

What is this test?

Back 18

D test

Tests inducible clindamycin induction
(Clinda can be induced to resistant when certain enzymes are present. Must to D test for all organisms resistant to erythromycin but susceptible to clinda)

Report as resistant by induction

Front 19

Is this a positive D test?

Back 19

NO.

Report at susceptible by induction

Front 20

All enterococcus is naturally resistant to?

Back 20

Cephalosporins
Clindamycin
TMP/SXT

Front 21

How to treat enterococcus endocarditis?

Back 21

AMP & GENT

Enterococcus shows SYNERGY with aminoglycosides

Front 22

What drugs do we use to treat VRE?

Back 22

Linezolid,
Synercid

Front 23

What is the mechanism of resistance in VRE?

Back 23

Plasmid mediated; bypasses metabolic block

Front 24

What organisms can have ESBLs?

Back 24

E coli
Proteus
Klebsiella

Front 25

Mechanism of resistance in ESBL?

Back 25

mobile plasmids!

Front 26

If ESBL is detected, what should you report? treat with?

Back 26

Report as R to all cephalosporins and penicilins
Cephalomycins ARE susceptible (Cephamycin)
Treat with Imipenem; Pip/Tazo (blocks B lactamase function)

Front 27

Test for ESBL?

Back 27

Double disk test

(Organism will be resistant to cephalosporin, but SUSCEPTIBLE to cephalosporin PLUS clavulinic acid

Front 28

What is a KPC?

Back 28

Klebsiella producing carbapenemase
BIG PROBLEM!

No drugs to treat this! Resistant to carbapenems and B lactamases

Front 29

Test for a KPC? (which ones are KPCs?

Back 29

Modified Hodge Test

A, B, E are KPCs: they hug the disk
(subjective. best test is molecular...)

Front 30

How do we test S. pna resistance to PCN?

Back 30

OXACILLIN! (because more sensitive)
- If resistant, confirm with MIC testing

Or could just do MIC testing as first step (but many smaller labs cannot)

Front 31

What is unique about S. pna PCN resistance?

Back 31

Different MIC values based on site!
CNS: R if greater than 2 mcg/ml
Resp or blood: 8 mcg/ml

Front 32

what is this

Back 32

Chlamydia. Old test - stain vacuoles with IODINE

Front 33

Chlamydia DFA - what is staining?

Back 33

ELEMENTARY BODIES!

Front 34

What is EIA and give an example of what organism it was used for?

Back 34

Enzyme immunofluorescence

C Diff! (though now use PCR. EIA was 60% sens!)

Front 35

What is endotoxin A in C Diff? B?

Back 35

Endotoxin A: Enterotoxin, FLUID

Endotoxin B: Cytotoxin

Front 36

What is the hypervirulent strain of C Diff?

Back 36

NAP1 strain

Front 37

What to do if your negative control is positive in an amplification?

Back 37

Contaminated! Invalid run. Cannot report results.

Must return to ORIGINAL specimen

Front 38

What is an internal amplification control?

Back 38

tests to see if amplification occurred in a specific patient (PATIENT SPECIFIC!)
Can have inhibitors (Vagisil, etc).
Invalidates PATIENT, not the whole run