Example Of Biology Essay

Antimicrobial Sensitivity

Results
In the experiment, antimicrobial effect of some important drugs was observed on S. Aureus using the Kirby Bauer method. Zone of inhibition was measured by placing chloramphenicol, streptomycin, ampicillin, erythromycin, kenamycin, rifampin, trimethoprim, and ciprofloxacin, in the agar plates having the microbe that was incubated for 24 hours at 37˚C. Thin veil of the outer portion of the zone of inhibition in the agar plate was not considered in the measurement of the diameter, as only the obvious zone in the outer margin was considered.
Figure 1: Kirby-Bauer disk diffusion method measuring zone sizes
All these antimicrobials showed different zone of inhibition against the microbe after the moisture is dried from the surface of both agar plates. Visually, the inoculated and incubated plate showed heavy concentration or cloudiness in the center of the plate with circles extending outwardly from the antibiotic discs. These circles are clear in color and obtained with the help of ruler. Results of the experiment presented the maximum zone of inhibition with the use of ampicillin disk. Ampicillin showed 40 mm zone of inhibition. Ciprofloxacin and rifampin also showed good results with 36 mm and 32 mm zone of inhibition respectively. Kanamycin and erythromycin showed 26 mm and 30 mm zone of inhibition respectively. Trimethoprim and streptomycin showed minimum results with 19 mm and 15 mm zone of inhibition respectively.

Results of the zones of inhibition have been presented in the following tables:

Comparisons of our obtained results with accepted standards (for susceptibility) are presented below:
Standard zone of inhibition for S. Aureus to show susceptibility against ampicillin is greater than or equal to 29 mm and our results are 40 mm.
Standard zone of inhibition for the microbe to show susceptibility against ciprofloxacin is greater than or equal to 21 mm and our results are 36 mm.
Standard zone of inhibition for the microbe to show susceptibility against chloramphenicol is greater than or equal to 18 mm and our results are 25 mm.
Standard zone of inhibition for the microbe to show susceptibility against streptomycin is greater than or equal to 15 mm and our results are also 15 mm.
Standard zone of inhibition for the microbe to show susceptibility against erythromycin is greater than or equal to 23 mm and our results are 30 mm.
Standard zone of inhibition for the microbe to show susceptibility against kanamycin is greater than or equal to 18 mm and our results are 26 mm.
Standard zone of inhibition for the microbe to show susceptibility against rifampin is greater than or equal to 20 mm and our results are 32 mm.
Standard zone of inhibition for the microbe to show susceptibility against trimethoprim is greater than or equal to 16 mm and our results are 19 mm.
Comparison of disk susceptibility testing pointed microbial susceptibility against all of the tested antimicrobials even though trimethoprim and streptomycin showed minimal zone of inhibition.