Detection of clinical isolates of tigecycline-resistant Escherichia coli harbouring tet(X4) in Myanmar

Objectives: Tigecycline is one of the last-resort antibiotics for treating serious infections caused by multidrug-resistant pathogens. This is the first report of clinical isolates of tigecycline-resistant Escherichia coli harbouring tet(X4) in Myanmar. Methods: Two E. coli isolates were obtained from two patients at two hospitals in Myanmar from November 2023 to May 2024. They were identified using MALDI-TOF MS, and minimum inhibitory concentrations (MICs) were determined using the broth microdilution method. Genomic DNA was extracted and sequenced using next generation sequencing. Drug resistance factors were determined, and the genetic environments surrounding tet(X4) and bla_NDM-5 were analysed. Conjugation rates of plasmids harbouring tet(X4) and bla_NDM-5 were calculated. Results: One strain, TGH62, was resistant to tigecycline (MIC 8 µg/mL) and meropenem (MIC 128 µg/mL), whereas the other, YGH433, was resistant to tigecycline (MIC 4 µg/mL). Whole-genome sequencing revealed that both strains harboured tet(X4) on plasmids and TGH62 also harboured bla_NDM-5 on a plasmid. The plasmids carrying tet(X4) in TGH62 and YGH433 belonged to the IncI and IncFII incompatibility groups, respectively. The plasmid carrying bla_NDM-5 belonged to the IncFIA incompatibility group. The conjugation efficiencies of the plasmids harbouring tet(X4) in YGH433 and bla_NDM-5 in TGH62 were relatively high, whereas that harbouring tet(X4) in TGH62 was low. Conclusions: Tigecycline-resistant Enterobacteriaceae harbouring tet(X4) may spread in hospitals in Myanmar. Further studies are needed to detect tet(X4) conferring tigecycline resistance in hospitals as well as environmental settings in Myanmar.