Emergence of tigecycline resistance in co-producing MCR-1 and NDM-5 during tigecycline salvage treatment.

OBJECTIVE

Here, we report a case of severe infection caused by that harbored , , and acquired resistance to tigecycline during tigecycline salvage therapy.

METHODS

Antimicrobial susceptibility testing, Southern blot hybridization, and complete genome sequence of the strains were carried out. The genetic characteristics of the and plasmids were analyzed. The whole genome sequencing of -containing plasmid was completed. Finally, putative single nucleotide polymorphisms and deletion mutations in the tigecycline-resistant strain were predicted.

RESULTS

Three isolates were obtained from ascites, pleural effusion, and stool of a patient; they were resistant to almost all the tested antibiotics. The first two strains separated from ascites (E-FQ) and hydrothorax (E-XS) were susceptible to amikacin and tigecycline; however, the third strain from stool (E-DB) was resistant to tigecycline after nearly 3 weeks' treatment with tigecycline. All three isolates possessed both and . The gene was found on the IncX3 plasmid, whereas the , and were located on the IncHI2 plasmid. Mutations in and were the reason for the resistance to tigecycline.

CONCLUSION

This is the first report of a colistin-, carbapenem-, and tigecycline-resistant in China. Tigecycline resistance acquired during tigecycline therapy is of great concern for us because tigecycline is a drug of last resort to treat carbapenem-resistant Gram-negative bacterial infections. Furthermore, the transmission of such extensively drug-resistant isolates may pose a great threat to public health.