Comparison of the Antibiotic-Resistant <i>Enterobacteriaceae</i> Content in Conventional, Organic and Fresh-Cut Vegetables Sold in Valencia (Spain)

Abstract

Bacterial content of fresh vegetables that are often eaten raw represents a risk factor for consumers, and the presence in these produce of antibiotic-resistant bacteria constitutes an additional food safety concern. We have compared the Enterobacteriaceae content, as well as the antibiotic resistances of bacterial isolates, in samples of different types of fresh vegetables (conventional an organic produce, fresh-cut vegetables and prepared salads) marketed in Valencia (Spain) in order to find possible differences among these vegetable types. Bacterial isolation, identification and resistance assays to eleven relevant chemotherapeutics agents were performed according to standard microbiological procedures. A total of 195 bacterial isolates (from 230 vegetable samples) were compared. All vegetable types carry a variety of opportunistic bacterial pathogens, with a significant frequency of resistant isolates to one or more (up to three, four or five antibiotics, depending on the vegetable type). Enterobacter spp. (mainly E. cloacae) and Klebsiella spp. (K. oxytoca and K. pneumoniae) were the most frequent in conventional, fresh-cut vegetables and prepared salads (60-77% of isolates), whereas in organic produce the most frequent species were Pantoea agglomerans (24%), Serratia marcescens (16%) and E. cloacae (13%). Fresh-cut produce had the highest content of bacterial burden and bacterial diversity, indicating that the sanitizing methods are not effective enough and should be improved. Organic vegetables showed a higher bacterial diversity and a lower frequency of antibiotic resistances, as compared with conventional produce, indicating that organic farming practices may favor microbial diversity and partially prevent selection and development of resistant bacteria. Therefore, it could be relevant to include the detection of antibiotic-resistant non-pathogenic Enterobacteriaceae species in fresh vegetables in the epidemiological surveillance routine to quantify dissemination of multi-resistances in non-hospital environment and to evaluate the potential role of consumption of fresh vegetables in spreading resistances into community.