Prevalence of Beta-lactamase producing Enterobacteriaceae in fresh vegetables

The persistence of antibiotic-resistant bacteria in the food chain is an important public health problem. Taking into account the scarcity of available data on fresh vegetables in comparison with those reported on animal products, this study was conducted to determine the importance of vegetables consumed raw as vehicles of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae, along with other β-lactamases.

We studied 133 fresh-vegetable samples (lettuce, curly endive, carrot, parsley, tomato, cucumber, pepper and strawberry) and 39 samples from the farm environment (air, water, handler and soil). Enterobacteriaceae and E. coli numbers were counted on CHROMagar Enterobacteria. The presence of antimicrobial-resistant enterobacteria was investigated from overnight streaking a loop from an overnight sample enrichment (Buffered Peptone Water) onto plates of CHROMagar ESBL, CHROMagar KPC, MacConkey agar and MacConkey agar supplemented with cefoxitin (16 µg/ml). Phenotypic confirmation of suspected isolates were performed by disk-based methods and through PCR (bla_CMY-2, bla_CTX-M, bla_TEM, bla_SHV, bla_NDM, bla_OXA-48 and bla_KPC genes).

The highest enterobacteria counts were found on parsley and curly lettuce (5,5±0,3 log cfu/g and 5,5±0,7 log cfu/g, respectively) with no correlation to the detection of antimicrobial-resistant isolates (182). Among them, the detected resistant-genes were bla_CMY-2 (nine strains), bla_CTX-M (three strains), and bla_NDM (two strains). Four strains, isolated from four tomato samples (4/133; 3,0%), were confirmed as ESBL-producers. These strains were identified as Enterobacter cloacae (3) and Serratia fonticola (1) by MALDI-TOF MS. No isolates produced carbapenemases or presented the AmpC-phenotype. Therefore, fresh vegetables could contribute to spread ESBL-producing enterobacteria along the food chain that may have relevance for human health.