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

Abstract

PurposeThe 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 methodsE. 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.ResultsOverall, 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.ConclusionThe 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.