Phenotypic and genotypic determination of β-lactamase-producing Escherichia coli strains isolated from raw milk and clinical mastitis samples, Mashhad, Iran

Abstract

A phenotypic and genotypic study was conducted on β-lactamase-producing Escherichia coli (E. coli) strains isolated from raw milk and clinical mastitis samples. A total of 86 raw milk samples and 51 clinical mastitis isolates were obtained. Multiplex polymerase chain reaction (M-PCR) was used to verify the presence of ESBL/AmpC related genes in E. coli. The raw milk and clinical mastitis E. coli strains were mostly resistant to ampicillin (82.25% and 52.94%, respectively) and trimethoprim/sulfamethoxazole (50% and 27.45%, respectively), so that multidrug resistance (MDR) was seen in 64.51% and 31.37% of raw milk and clinical mastitis isolates, respectively. The blaTEM (46.87%) and blaCTX-M-14 (43.75%) genes were the most common genes in the raw milk samples. Regarding clinical mastitis samples, the most dominating gene was blaCTX-M-3 (36.36%). In conclusion, raw milk can be a potential source of E. coli carrying resistance genes that may spread to the environment and food chain.