Bacteria con leche: Bacterial populations and antibiotic resistance within conventional, USDA organic, and local milk

Wilson, Kristen M. (2014) Bacteria con leche: Bacterial populations and antibiotic resistance within conventional, USDA organic, and local milk. Undergraduate thesis, under the direction of Colin Jackson from Biology, The University of Mississippi.

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Abstract

Concerns over food production and processing, along with increasing outbreaks of foodborne illnesses and antibiotic resistant infections have led many consumers to seek alternative food sources in the organic and local food markets. This study compared conventional, USDA certified organic, and local “farmer’s market” milk types to determine whether there is any noticeable benefit to purchasing organic or locally harvested milk in terms of their bacterial populations and level of antibiotic resistance. Samples from various milk types were plated on Tryptic Soy Agar and Milk Agar plates to enumerate bacteria, and the cultivated bacteria tested for resistance to the antibiotics penicillin, erythromycin, tetracycline, and gentamicin. Bacterial cultures from the various milk samples were identified using 16S rRNA gene sequencing. Local farmer’s market milk had the most abundant and diverse bacterial composition, containing several potential pathogens, and a high general level of antibiotic resistance. Conventional milk samples also showed considerable bacterial counts and high levels of antibiotic resistance. On the other hand, USDA certified organic milk yielded no culturable bacteria on either TSA or MA plates. This study shows that concerned with food safety should consume USDA organic milk to lessen their exposure to high numbers of antibiotic resistant and potentially pathogenic bacteria.

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