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

Abstract

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 <i>tet</i>(X)-harboring <i>Acinetobacter</i> isolates (8.9%, <i>n</i> = 180) from 2,018 samples collected from avian farms and adjacent environments in China. Eighteen <i>tet</i>(X)-harboring isolates (10.0%) were found to cocarry the carbapenemase gene <i>bla</i>_NDM-1, mostly from waterfowl samples (94.4%, 17/18). Interestingly, among six <i>Acinetobacter</i> strains, <i>tet</i>(X) and <i>bla</i>_NDM-1 were found to colocalize on the same plasmids. Moreover, whole-genome sequencing (WGS) revealed a novel orthologue of <i>tet</i>(X) in the six isolates coharboring <i>tet</i>(X) and <i>bla</i>_NDM-1 Inverse PCR suggested that the two <i>tet</i>(X) genes form a single transposable unit and may be cotransferred. Sequence comparison between six <i>tet</i>(X)- and <i>bla</i>_NDM-1-coharboring plasmids showed that they shared a highly homologous plasmid backbone even though they were isolated from different <i>Acinetobacter</i> species (three from <i>Acinetobacter indicus</i>, two from <i>Acinetobacter schindleri</i>, and one from <i>Acinetobacter lwoffii</i>) from various sources and from different geological regions, suggesting the horizontal genetic transfer of a common <i>tet</i>(X)- and <i>bla</i>_NDM-1-coharboring plasmid among <i>Acinetobacter</i> 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.