Investigation of tigecycline resistant Escherichia coli from raw meat reveals potential transmission among food-producing animals

Abstract To investigate the characteristics of tet(X4)-carrying E. coli from retail raw meat, three hundred and eleven retail raw meat samples including chicken, pork, duck, and beef were collected for screening for tigecycline resistant isolates in Sichuan Province, China. We detected 25 (8.0%, 95%CI: 5.3%–11.6%) tet(X4) positive E. coli isolates from 311 retail meat with the highest prevalence (13.4%, 95%CI: 7.3%–21.8%) observed in pork. All the isolates were analyzed by antimicrobial susceptibility testing, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE), conjugation experiments, and whole genome sequencing (WGS) were performed to study the phylogenetic relationship and genomic characteristics of the tet(X)-carrying isolates. Conjugation and S1-PFGE profiling showed 6 isolates (24.0%) successfully transferred the resistant phenotype with frequencies from 3.63 × 10−5 to 7.68 × 10−2. Simultaneously, tet(X4), floR, and the characteristic structure of adjacent abh gene and cassette flanked by ISCR2 were identified in all 25 isolates, and a structure of abh-tet(X4)-ISCR2-virD2-floR was aligned as an important genetic pattern around tet(X4). Two dominant sequence types (STs) ST1638 (n = 4) and ST48 (n = 4) were identified by in silico MLST. Single nucleotide polymorphisms analysis revealed two potential clone-like transmission clusters which showed high concordance with the local spatio-temporal epidemiology, suggesting that clonal transmission events were very likely. The presence of tet(X4) in multiple different clone complexes (CCs) and the identification of two clone-like transmission indicates its potentially extensive and successful spread among different food-producing animals.