Epidemiology and resistance mechanisms of tigecycline- and carbapenem-resistant in China: a multicentre genome-based study.

OBJECTIVES

To elucidate the molecular epidemiology of tigecycline and carbapenem-resistant isolates and mechanisms of tigecycline resistance.

METHODS

We gathered 31 unduplicated strains of tigecycline-resistant from six hospitals nationwide. Antimicrobial susceptibility testing, phenotypic detection, and PCR identification were performed first, followed by homology analysis using MLST and PFGE. Conjugation transfer experiments using resistance gene plasmids were carried out, and the conjugates' growth curves were examined. All strains were sequenced using the Illumina HiSeq technology, and we identified a strain KP28 carrying a complete gene cluster . Then, its plasmid was further constructed using the PacBio platforms to complete the frame. The genetic connection of the gene cluster carried by KP28 was established using core genome analyses.

RESULTS

All 31 tigecycline-resistant strains (TG-CRE) were multidrug resistant. PFGE classified strains of CRKP, CRECL, and CRKAE into 16 distinct spectra, 6 distinct spectra, and 3 distinct spectra. MLST results showed a high concentration of ST11 in CRKP strains and a predominance of ST116 in CRECL strains, suggesting possible clonal transmission or selective dominance. The findings of the plasmid conjugation assay revealed that three strains expressing carbapenem resistance genes were effectively transmitted to the recipient cell EC600. WGS data revealed that these 31 strains include 79 resistance genes, with one strain (KP28) carrying the whole tigecycline resistance gene cluster, . This resistance gene is contained in a large IncHI5 plasmid, which is difficult to transfer.

CONCLUSION

The overall carriage rate of the gene cluster was found to be low among the five Chinese hospitals investigated. Conversely, (A) mutations were present in most of the strains. Bacteria with the carbapenem resistance genes and are vulnerable to horizontal transmission. Increasing the risk of transmission of antibiotic-resistant genes.