High incidence of multidrug-resistant Escherichia coli coharboring mcr-1 and blaCTX-M-15 recovered from pigs

High incidence of multidrug-resistant Escherichia coli coharboring mcr-1 and blaCTX-M-15 recovered from pigs Muhammad Shafiq,1 Jinhu Huang,1 Sadeeq Ur Rahman,2 Jan Mohammad Shah,1 Li Chen,1 Yi Gao,1 Mengli Wang,1 Liping Wang11Moe Joint International Research Laboratory of Animal Health and Food Safety, Laboratory of Veterinary Pharmacology and Toxicology, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, People’s Republic of China; 2College of Veterinary Sciences and Animal Husbandry, Section Microbiology, Abdul Wali Khan University, Mardan, KP, PakistanPurpose: The coexistence of mobile colistin (COL)-resistant gene mcr-1 with extended-spectrum beta-lactamase (ESBL) gene in Escherichia coli has become a serious threat globally. The aim of this study was to investigate the increasing resistance to COL and in particular its coexistence with ESBL-producing E. coli recovered from pig farms in China.Materials and methods: E. coli were isolated from 14 pig farms in Jiangsu China. Susceptibility testing was identified by micro-dilution method. PCR assay and nucleotide sequencing were used to detect COL-resistant genes, mcr-1 to −5, as well as ESBL genes, blaCTX-M, blaSHV and blaTEM. Conjugation experiment, plasmid replicon typing of the multidrug resistance (MDR), S1-PFGE and DNA southern hybridization were performed to study the transferability of these genes.Results: Overall, 275 E. coli isolates were recovered from a total of 432 cloacal and nasal swabs. More than 90% of the isolates were MDR, of which 70.18% were resistant to COL. Of these 275 isolates, mcr-1 was identified as the most predominant gene carried by 71.63% (197/275) of isolates, 39.59% (78/197) of the isolates were harboring both mcr-1 and ESBL genes (blaCTX-M, blaSHV and blaTEM). ESBL genotyping showed that blaCTX-M was the most predominant ESBL (68.49%) followed by blaSHV (16.4%) and blaTEM (15%). Sequencing revealed that the most common variants of blaCTX-M identified were, blaCTX-M-15 (69%), blaCTX-M-55 (29%) and blaCTX-M-1 (1.8%). IncHI2, IncFIB, IncFIC, IncN and IncX4 were found to be the most common Inc-types found both in donors and in transconjugants and were associated with the transfer of the mcr-1 and ESBL encoding genes. Six strains carried a total of five different plasmids: approximately 97-, 130-, 160-, 227- and 242-kb plasmids.Conclusion: The coexistence of the mcr-1- and blaCTX-M-15-carrying isolates displaying high MDR, recovered from E. coli of pig origin, is a major concern for both humans and veterinary medicine.Keywords: E. coli, colistin, mcr-1, ESBL, coexistence