Extended-Spectrum -Lactamase, AmpC, and MBL-Producing Gram-Negative Bacteria on Fresh Vegetables and Ready-to-Eat Salads Sold in Local Markets

We investigated the occurrence of extended-spectrum -lactamase (ESBL), AmpC, and carbapenemase-producing Gram-negative bacteria isolated from 160 samples of fresh vegetables (n=80) and ready-to-eat (RTE) prepacked salads (n=80). Phenotypic and genotypic analyses were carried out on the isolates in terms of the species present and relative resistance. Resistance to -lactam antibiotics was found in only 44 (24 from fresh vegetables and 20 from RTE salads) of a total of 312 Gram-negative strains (14.1%). The prevalence of ESBL-producing strains from fresh vegetables was 83.3% (20/24) and 16.7% (4/24) for AmpC. Among the 20 bacterial isolates from RTE salads, 80% (16/20) were identified as ESBL-producing strains and the remaining 20% (4/20) as MBL-producing strains. PCR and sequencing confirmed the presence of bla(SHV-12), bla(CTX-M-1), bla(CTX-M-15,)bla(RHAN-1), bla(ACC-1), bla(DHA-1), bla(VIM-1), and bla(IMP-1). Seven different replicons were identified, where IncHI1, FIA, and I1 were the most representative types; when compared with the Inc types, isolates from fresh vegetables and RTE salads were similar. The location of genes on a conjugative plasmid was confirmed by positive results obtained with conjugation assays. Our study has demonstrated the occurrence and distribution of ESBL/AmpC and MBL strains in fresh vegetables and RTE salads in Italy and possible public health risks associated with consumption of these fresh products.