Bacteria ID & AntiB Testing

Question 1

Mac Conkey agar plate:
It contains bile salts that do not allow the growth of gram + bacteria and has a color change for bacterial colonies that ferment lactose.
What kind of media is Mac Conkey agar?

Answer 1

Selective & differential

Question 2

T/F: A catalase test is positive if the reaction is bubbling

Answer 2

True

Question 3

Briefly describe how the catalase test is performed AND which groups of bacteria it is used to differentiate

Answer 3

A drop of hydrogen peroxide (H2O2) is added to a bacterial sample on a slide. If bubbles occur, the bacteria contain catalase enzyme.
Examples of catalase positive organisms include: Staphlococcus, E. coli and Pseudomonas.

Question 4

T/F: The effectiveness of an antiB depends on multiple different factors including the ability of the antiB to reach the site of infection

Answer 4

True

Question 5

An antiB that kills bacteria is called ___
An antiB that prevents the bacteria from multiplying is ___

Answer 5

Bactericidal
Bacteriostatic

Question 6

Name two reasons for testing antiB susceptibility of bacteria

Answer 6

1. Choose the best antibiotic to eliminate the bacteria from the patient. Understanding cost, side effects, and ability to deliver drug to area of infection are considerations when choosing “best.”
2. Avoid using antibiotics that will be less effective and may promote bacterial resistance.
3. Avoid using antibiotics that will not be effective in eliminating bacteria from patient.
4. Research purposes to monitor development of bacterial resistance of a genus of bacteria over time.

Question 7

Briefly describe the procedure of a Kirby Bauer/disc agar diffusion method of antibiotic susceptibility testing and how a technician interprets the results.

Answer 7

• AntiB discs are planted on a lawn of bacteria on agar plate
• Effective antiB will cause a ring of “non-growth” around disc
• Tech will measure the zone of inhibition & utilize the chart to determine effectiveness (sensitive, resistant, intermediate)
• Chart use is mandatory!

Question 8

T/F: Larger zone of inhibition around one antiB disc always indicates more susceptibility than around another disk

Answer 8

False

Question 9

T/F: Lower MIC is an indication of a better antimicrobial agent

Answer 9

True