Co-occurrence of Plasmid-Mediated Tigecycline and Carbapenem Resistance in Acinetobacter spp. from Waterfowls and Their Neighboring Environment.

Tigecycline serves as one of the antibiotics of last resort to treat multidrug-resistant (including carbapenem-resistant) pathogens. However, the recently emerged plasmid-mediated tigecycline resistance mechanism, Tet(X), challenges the clinical efficacy of this class of antibiotics. In this study, we detected 180 (X)-harboring isolates (8.9%,  = 180) from 2,018 samples collected from avian farms and adjacent environments in China. Eighteen (X)-harboring isolates (10.0%) were found to cocarry the carbapenemase gene , mostly from waterfowl samples (94.4%, 17/18). Interestingly, among six strains, (X) and were found to colocalize on the same plasmids. Moreover, whole-genome sequencing (WGS) revealed a novel orthologue of (X) in the six isolates coharboring (X) and Inverse PCR suggested that the two (X) genes form a single transposable unit and may be cotransferred. Sequence comparison between six (X)- and -coharboring plasmids showed that they shared a highly homologous plasmid backbone even though they were isolated from different species (three from , two from , and one from ) from various sources and from different geological regions, suggesting the horizontal genetic transfer of a common (X)- and -coharboring plasmid among species in China. Emergence and spread of such plasmids and strains are of great clinical concern, and measures must be implemented to avoid their dissemination.