Antibiotic Sensitivity

MBK – Lab Report Name: ____________________

Section: ___________________

Antibiotic Sensitivity

The Kirby-Bauer Test

Interpret your results as described below.

INTERPRETATION: · Place the metric ruler across the zone of inhibition, at the widest diameter, and measure from one edge of the zone to the other edge. HOLDING THE DISH UP TO THE LIGHT MIGHT HELP.

· The disc diameter will actually be part of that number.

· If there is NO zone at all, record it as 0---even though the disc itself is around 7 mm.

· Record your zone diameter in millimeters.

· Find the zone on the chart which follows and determine if S. epidermidis is sensitive, resistant, or intermediate.

Questions:

A. Define the term “selectively toxic.” Why is it an important feature of antimicrobial agents?

B. What are broad and narrow spectrum antimicrobials? What are the pros and cons of each?

C. What is direct selection?

D. What is the difference between and antibiotic and an antimicrobial chemical?

E. What is the mode of action for each of the following:

a. Bacitracin: b. Nystatin: c. Tetracycline: d. Ciprofloxin:

F. Describe three mechanisms by microbes might become resistant to the action of an antimicrobial drug?

G. Why do you think that neglecting to finish a prescribed course of antibiotics might contribute to the rise of antibiotic resistance?

H. What is a tube dilution test, how is it used to determine susceptibility?

I. Define the following: a. Minimum Inhibitory Concentration (MIC) b. Zone of Inhibition

J. What were the results of your Kirby-Bauer test for S.