Frequency of extended-spectrum β-lactamase (ESBL)- and AmpC β-lactamase-producing Enterobacteriaceae in a cheese production process

The aim of this study was to investigate the extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase activities of Enterobacteriaceae isolated from raw milk and cheese production line and to determine the probability of transmitting these bacteria to consumers. One hundred seventy-three samples from raw milk and cheese production lines were analyzed; 64 isolates were confirmed as Enterobacteriaceae. Sixteen of 64 isolates (25%) were resistant to at least one cephalosporin according to European Committee on Antimicrobial Susceptibility Testing Standards (EUCAST) and Clinical and Laboratory Standards Institute criteria. Seven of the 16 resistant isolates (43.75%) had confirmed ESBL activity. Additionally, phenotypic AmpC β-lactamase activity was observed in 31 (48.44%) of 64 Enterobacteriaceae isolates and confirmed in 27 of the 31 strains (89.1%). Overall, 3 isolates showed both ESBL activity and AmpC resistance, 28 isolates were only AmpC resistant, and 5 isolates had ESBL activity alone. Of the 173 samples, the proportions of samples that contained ESBL- and AmpC-producing isolates were 4.64 and 15.6%, respectively. Five of the ESBL-positive isolates (62.5%) and 11 of the AmpC-positive isolates (40.7%) were obtained from bulk milk tanks; therefore, the bulk tank plays a very important role in the spread of antibiotic-resistant bacteria. Periodic cleaning and maintenance of bulk tanks should be performed and recorded. Effective food safety and hygiene practices should significantly reduce cross-contamination in dairy plants.