Emergence of the resistance-nodulation-division efflux pump tmexCD3-toprJ3 gene confers resistance to tigecycline in Pseudomonas juntendi and Proteus terrae isolated from a pig farm in China.

Abstract

Tigecycline is regarded as a last-resort antimicrobial agent against multidrug resistance (MDR). However, resistance-nodulation-division efflux pump resistance genes, such as tmexCD3-toprJ3, that confer resistance to tigecycline have emerged. This study aimed to characterise the tmexCD3-toprJ3 gene cluster in Pseudomonas juntendi and Proteus terrae isolated from a pig farm. Samples were obtained from a Chinese piggery and included 92 pig faecal samples, 56 wastewater samples, 23 drinking water samples, 28 sow vagina samples and nine sow uterus swabs. The presence of tmexCD3-toprJ3 was detected using a polymerase chain reaction assay, and the antimicrobial susceptibility profile of the tmexCD3-toprJ3-positive isolates was determined using the broth dilution method. Genomic locations were identified using whole-genome sequencing and bioinformatics. We identified two tmexCD3-toprJ3-positive isolates, and both isolates were highly resistant to antibiotics such as tigecycline. In addition, we identified several mobile elements (ISPa7, ISCfr1, ISVsa3) and insertion sequences (TnAs2, TnAs3) in tmexCD3-toprJ3-positive isolates that could increase the potential for the spread of MDR. To the best of our knowledge, this study is the first to report the detection of tmexCD3-toprJ3 in P. juntendi and P. terrae isolated from a pig farm.