Faculty Sponsor

Dr. Sarah Boomer


Raw ground beef purchased at supermarkets across America have one thing in common: they harbor bacteria, some of which are drug resistant and can be detrimental to public health. To understand the impact of farming and processing practices on the quantity of bacteria and drug resistance, organic and regular beef were assessed using MacConkey media. Bacterial colonies were sorted according to lactose utilization, with positive colonies representing fecal E. coli. Lactose negative colonies were further characterized into one of two groups (fecal Hafnia-like or soil Pseudomonas) using a variety of metabolic tests (oxidase, sulfur, indole). Advanced metabolic testing showed that regular beef contained significantly more fecal E. coli-like bacteria, Hafnia-like bacteria and fecal Providencia-like bacteria than organic beef. Soil Pseudomonas was only isolated from regular beef. This procedure was repeated using MacConkey plates containing commonly used agricultural antibacterial drugs to assess the prevalence and types of drug-resistant bacteria. Bacteria resistant to penicillin, sulfamethazine, cefazolin, or ampicillin were found at significantly higher levels on regular beef than organic. Bacteria resistant to more than one of these drugs were only found on regular beef.

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