AmpC- and Extended-Spectrum β-Lactamase–Producing Enterobacteriaceae Detected in Fresh Produce in Central Ohio

Abstract

Salad vegetables purchased from farmer's markets and grocery stores in central Ohio during the summers of 2015 and 2016 were tested for the presence of Enterobacteriaceae resistant to extended-spectrum cephalosporins and carbapenems, Salmonella contamination, and coliform bacterial counts. A total of 364 samples were collected from 36 farmers' markets and 33 grocery stores. Using selective media, we found 23 (6.3%) samples that produced Enterobacteriaceae expressing an AmpC β-lactamase phenotype, with 11 (3.0%) confirmed to contain blaCMY and 6 (1.6%) that produced Enterobacteriaceae with an extended-spectrum β-lactamase (ESBL) phenotype, 1 (0.3%) of which was confirmed to contain blaCTX-M. All blaCMY and blaCTX-M strains were isolated from leafy greens. No Salmonella spp. or carbapenem-resistant Enterobacteriaceae were recovered from fresh produce samples. Adjusting for year, the geometric mean coliform count differed (P < 0.05) between produce types, with the count in tomatoes (15 CFU/mL) being lower than those in cucumbers (77.4 CFU/mL) and leafy greens (75.0 CFU/mL). The coliform counts also differed (P < 0.05) between years, with 19.6 CFU/mL in 2015 and 96.0 CFU/mL in 2016. There was no difference in coliform counts or the prevalences of Enterobacteriaceae expressing AmpC or ESBL phenotypes in produce purchased from farmers' markets and grocery stores.