Purpose: A greenhouse study was carried out to determine the effect of application of composted manure, originating from cattle with or without antibiotic administration, on ARB found on the surface of radish taproots.
Methods: Manure was collected from treated and non-treated beef cattle (chlortetracycline, sulfamethazine, and tylosin) or dairy cattle (cephapirin and pirlimycin). Composting procedures followed the FDA Food Safety Modernization Act (FSMA) guidelines. Manures and composts were applied to locally-sourced soil. Radishes (n = 3) were grown to maturity, and the surfaces of the taproots were plated onto R2A containing clindamycin, ceftazidime, erythromycin, tetracycline, sulfamethoxazole, vancomycin, or no antibiotics to enumerate heterotrophic ARB.
Results: Radishes grown without soil amendment had fewer ceftazidime-resistant bacteria than those grown in soil amendments originating from beef (P < 0.02) or dairy (P < 0.04) cattle. Radishes grown in either compost also had more ceftazidime-resistant bacteria than those grown without soil amendment (P < 0.006). Radishes grown in beef compost and beef manure had greater tetracycline-resistant bacteria than those grown in dairy compost and dairy manure (P < 0.01). Tetracycline-resistant bacteria on radishes grown in manure were fewer than on radishes grown in compost (P < 0.02) and no soil amendment (P < 0.05).
Significance: This study can determine whether composted manure can be a source of ARB on fresh produce, providing insight as to how agricultural practices could spread ARB from the environment to humans. Strategies using practices, like those outlined in the FSMA produce rule, could reduce consumer exposure to ARB.