Acquisition of cephalosporin resistance genes blaCTX-M-55, blaCTX-M-65, and blaCMY-2 leads to quinolone resistance in colistin-resistant Escherichia coli harboring mcr-1 gene

Abstract

Food contamination with plasmid-mediated antibiotic-resistant Escherichia coli has not been thoroughly investigated. This study aimed to clarify the prevalence of colistin-resistant AmpC/extended-spectrum β-lactamase (ESBL)-producing E. coli harbouring mcr (COL-ESBL-EC) and to determine antibiotic resistance by comparison with AmpC/ESBL-producing E. coli (ESBL-EC) and colistin-resistant E. coli harbouring mcr (COL-EC). Sixty chicken meats were tested for COL-ESBL-EC contamination. The result showed that 64 COL-ESBL-EC were isolated from 66.7% of the samples, and compared with ESBL-EC and COL-EC were isolated before. The genotypes of the COL-ESBL-EC showed blaCTX-M-55/TEM, blaCTX-M-55, blaCMY-2, and blaCTX-M-65 were predominant. The COL-ESBL-EC results showed a similar trend for blaCTX-M identification to that of ESBL-EC. The mcr was investigated, and mcr-1 was detected in COL-ESBL-EC and COL-EC. Antibiotic susceptibility testing revealed that many strains of COL-ESBL-EC and ESBL-EC were resistant to quinolones, and fosfomycin (FOS). These results suggest that COL-ESBL-EC has simultaneously acquired AmpC/ESBL-related, quinolone, and FOS resistance genes in COL-EC.