Georgia Journal of Science

Article Title



Antibiotic resistance severely affects the control of bacterial infections. The increased prevalence of antibiotic usage has contributed to the problem of resistance. Pseudomonas aeruginosa is a gram-negative bacterium often encountered in serious opportunistic infections. This experiment was performed to determine if antibiotic resistance can be induced in P. aeruginosa after repeated exposure to the antibiotic gentamicin. A Pseudomonas aeruginosa culture was challenged to four rounds of exposure to 10 µg of Gentamicin over a 6 week period. Each round occurred as follows: Five 10 mL Brain-Heart Infusion (BHI) broths containing a 10 µg disc of Gentamicin were inoculated with P. aeruginosa. After 36 hrs of incubation at 37° C, bacteria from each broth tube was streaked onto a different Blood Agar Plate and incubated for an additional 24 hrs at 37° C. Bacteria from each plate were introduced into 10 mL of Phosphate-Buffered Saline (PBS) matching turbidity to a 0.5 McFarland Standard. Bacteria from each PBS tube was swabbed onto its own Mueller-Hinton Plate and a Kirby-Bauer Test was performed using one disc of 10µg Gentamicin per plate. Zones of inhibition were then measured after 24 hours. Bacteria were then scraped from the edge of each zone and introduced into the next set of BHI tubes for the next round of antibiotic challenge. This was repeated for all four rounds. In addition, Kirby-Bauer tests were performed using unchallenged P. aeruginosa. These were used as a control. The data showed that the mean zone of inhibition of the control bacteria was 25 mm, while those of the four succeeding rounds of gentamicin challenge were 21.2 mm, 19.4 mm, 14.6 mm, and 9.8 mm respectively. Pairwise t-tests show highly significant decreases from round to round (p < 0.01). Resistance increased significantly with each subsequent exposure, reinforcing concern about overusage of antibiotics.


YHC Biology Dept., Dr. Andrea Kwiatkowski

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