Occurrence and characteristics of Escherichia coli mcr-1-like in rabbits in Shandong, China.

Polymyxin is regarded as the last retort to fight against multidrug-resistant (MDR) Enterobacteriaceae. The emergency and spread of polymyxin-associated resistance gene mcr-1 evoked great panic of no medicine to cure the bacterial infection in society. mcr-1 is widespread in domestic and wild animals. Therefore, continuous monitoring of its prevalence and characteristics is required. In this study, we used a polymerase chain reaction (PCR)-based method to detect the mcr-1 of Escherichia coli isolated from rabbits of Tai'an, China, and determined the characteristics of mcr-1-bearing plasmids. A total of 55 non-duplicated E. coli was recovered from the swabs of rabbit faeces. Plasmid profiling, plasmid and chromosome PCR, complete genome sequencing, a conjugation experiment, lactose fermentation experiment, multilocus sequence typing and polymyxin resistance tests were performed to determine the characteristics of mcr-1-bearing plasmids. 14.6% (8/55) of the specimens were mcr-1 positive. The mcr-1-positive E. coli harboured more drug-resistant genes compared with the mcr-1-negative specimens, and results showed four sequence types. Overall, these findings suggested the possible threat of the transmission of mcr-1 from rabbits to humans, especially since the gene is located on transferable plasmids making horizontal transfer relatively easy. Since food-producing animals are necessary for our daily diet, worldwide cooperation is needed in fighting the spread of this drug resistance gene to avoid human infections with MDR pathogenic bacteria.