Kirby Bauer Technique

Chemotherapeutic Agents

Antibiotics

Antibiotic resistance

http://www.fda.gov/oc/opacom/hottopics/anti_resist.html

http://whyfiles.org/038badbugs/

http://www.cdc.gov/drugresistance/

http://www.cdc.gov/drugresistance/community/ - Get Smart about Antibiotic Use

Introduction – Chemotherapeutic agents are chemical substances used in the treatment of infectious diseases  Their mode of action is to interfere with microbial metabolism; thereby produing a bacteriostatic or bacteriocidal effect on the microorganisms, without producing a like effect on the host cells.

Antibiotics are synthesized and secreted by some true bacteria, actinomycetes, and fungi.  These molecules are designed in nature to inhibit or prevent the growth of other microorganisms in the environment.  Today, antibiotics have been designed or modified based on this basic principle.  There are other synthetic drugs produced through drug research that are capable of inhibiting bacterial growth.

Antibiotics act in two basic ways:  prevention of cell wall or cell membrane construction and interference with the process of cell protein synthesis.  Because there are multiple steps in the process of protein synthesis, antibiotics can block any step in this process and effectively eliminate the bacteria.

Mataerials and Methods-

Materials

• Agar plate
• Inoculating loop
• Forceps
• Antibiotic disks

Methods

1. Divide the petri dish in half
2. Use aseptic technique to transfer your bacteria from the stock plate to your experimental plate
3. Streak a Gram + bacterium on one side( Streptococcus mutans, Staphylococcus saprophyticus, Saphylococcus epidermidis, or Bacillus subtilis)
4. Streak a Gram – bacterium on the other side( E. coli)
5. Flame your forceps. 
6. Place a disk in the middle of each side of the Petri Dish
7. Tap the disk down to make sure that it stays in place.
8. Incubate the plates overnight at 37^oC
9. Measure the zone of inhibition .   Place a ruler over the clear area around the disk.  Measure the diameter. 
10. Record in your data chart.  Refer to the chart and determine whether the bacterium is sensitive or resistan

Reference Chart

Conclusions –

1.        Based on your recent Internet research, why is there an antibiotic crisis?

2.       Why is the Kirby- Bauer test important to physicians and patients?

3.       What have your learned from your unit on Microbiology?