A New Twist to the Kirby-Bauer Antibiotic Susceptibility Test Activity—Increasing Antibiotic Sensitivity of <italic toggle="yes">Pseudomonas fluorescens</italic> through Thermal Stress

Abstract

Antibiotic sensitivity and the effect of temperature on microbial growth are two standard laboratory activities found in most microbial laboratory manuals. We have found a novel way to combine the two activities to demonstrate how temperature can influence antibiotic sensitivity using a standard incubator in instructional laboratory settings. This activity reinforces the important concepts of microbial growth and temperature along with Kirby-Bauer antibiotic susceptibility testing. We found that Pseudomonas fluorescens can be manipulated to become more sensitive to several antibiotics by simply increasing growth temperature and exposing the organism to various antibiotics. No additional equipment is required beyond a standard incubator. Pseudomonas fluorescens is an excellent choice for this activity since it is a safe alternative to Pseudomonas aeruginosa, a biosafety level 2 agent. Pseudomonads are important to explore in the microbiology laboratory since Pseudomonas aeruginosa poses a serious issue in health care settings, as this organism is known to be a multi-drug-resistant pathogen (6). More importantly, P. fluorescens is a good alternative in the laboratory to P. aeruginosa since it is also pigmented (5) and a possible reservoir of antibiotic resistance genes (4). In addition, it grows best at room temperatures and can easily be thermally stressed by placing in a standard 35ºC to 37ºC incubator