Phenotypic and genotypic characteristics of Extended-Spectrum β-Lactamase (ESBL) Production and Colistin-resistance in Salmonella enterica and Escherichia coli Isolated from​ Pigs and their Meat Products in the Border Provinces between Thailand and Cambodia, Lao PDR and Myanmar

Abstract

A total of 809 samples of pig rectal swab from slaughterhouses (n=441) and pork from retail market (n=368) were collected in the border provinces among Thailand, Cambodia, Lao PDR and Myanmar between October 2016 and March 2017. The objective of this study was to determine resistance to extended-spectrum ß-lactams (ESBLs) and colistin in Salmonella enterica and Escherichia coli. A total of Salmonella (n=463) and E. coli (n=767) were collected and determined for the ESBL-production and for the Minimum Inhibitory Concentrations (MICs) of colistin and; the presence of ESBL gene and mcr gene. The results showed that the prevalence of Salmonella was highest in Cambodia (65.8%) and lowest in Myanmar (13.6%). Serovar Rissen was mostly observed. The prevalence of E. coli in pork was above 87% in all countries. ESBL-producing Salmonella (1.9%) and E. coli (6.3%) were detected at low level. Five bacterial isolates (1 Salmonella and 4 E. coli) were simultaneously resistant to colistin produced by ESBL enzymes. Among the ESBL genes tested, blaCTX-M and blaTEM genes were found in all countries. Twelve Salmonella and 68 E. coli isolates were positive to mcr-1 gene. One Salmonella and 31 E. coli isolates harbored mcr-3 gene. In addition, one Salmonella isolate from pork in Lao PDR carried both mcr-1 and blaCTX-M. One E. coli isolate from pigs in Thailand and one E. coli isolate from pig and pork in Cambodia belonged to mcr-3 and blaCTX-M. These findings demonstrated that pigs and pork serve as reservoirs for the next-generation cephalosporins and colistin-resistant Salmonella and E. coli. Monitoring of resistance to these antibiotics in food animals is needed.