Purpose: To investigate the frequency and antimicrobial susceptibility of Salmonella in vegetable and environmental samples at the production level as well as in post-harvest level.
Methods: Samples (n = 350) were collected from organic farms, farmers markets, organic and conventional supermarkets located in Washington D.C. or Maryland. Portions of each sample were diluted 1:9 (wt/vol) with buffered peptone water. After enrichment in Luria-Bertani broth containing 5% sheep blood, samples were streaked on XLT-4 agar; presumptive colonies were confirmed biochemically and through PCR analysis. Antimicrobial susceptibility testing was carried out using the agar dilution method described by the Clinical Laboratory Standards Institute. The data was analyzed using the χ² test.
Results: On organic farms surveyed, there was a significant (P = 0.01) difference in the occurrence of Salmonella between environmental, animal feces, animal feed and vegetable samples, with prevalence of 35%, 70%, 22% and 20%, respectively. There was no significant difference in the rates of antimicrobial resistance of Salmonella recovered from those environments. Further there was no significant difference in Salmonella prevalence and antimicrobial resistance between vegetables from organic markets, conventional markets, farmers markets and farms.
Significance: While the findings show contamination at the farm level is significantly different, factors contributing to antimicrobial resistance of vegetables were not clearly identified. These data also suggest that there is no difference in microbiological quality of organic vegetables compared to conventionally raised vegetables.