A simple method for measuring antibiotic resistance in a community of bacteria

Antibiotic resistant bacteria infiltrate drinking water, increase human exposure, and spread into clinical settings. Regulatory agencies need simple test for ARI to monitor environmental quality. This study is first to measure resistance in a consortium of bacteria, not pure cultures. Our rapid method – “In-the-zone” (ITZ) employs a) the size of zones of inhibition b) identity of bacteria in the zone c) number of resistant clones within zones of inhibition and d) type of antibiotic to compute ARI. Results can be obtained within 24 - 48 hrs with very little effort. This semester, we repeated the test and validated the weighting of various parameters. The ITZ assay yield consistent and reproducible data on zones of inhibition of bacteria community. The diameter of inhibition zones was the most important parameter distinguishing resistomes of varying ARI. Landfill, manured garden, and waste plant samples scored highest in antibiotic resistance index compared to beach sand.