Novel Plasmid-Mediated (X5) Gene Conferring Resistance to Tigecycline, Eravacycline, and Omadacycline in a Clinical Acinetobacter baumannii Isolate.

A novel, plasmid-mediated, high-level tigecycline resistance (X) gene variant, (X5), was detected in a clinical isolate from China in 2017. Tet(X5) shows 84.5% and 90.5% amino acid identity to Tet(X3) and Tet(X4), respectively, with similar binding sites and a comparable affinity for tetracyclines. The (X5)-containing plasmid could only be transferred to via electrotransformation. This report follows the recent study describing the identification of (X3) and (X4).