Emergence of Acinetobacter towneri harbouring a novel plasmid with bla and tet(X7) from hospital wastewater in the Philippines.

Objectives: The clinical effectiveness of carbapenem and tigecycline, which are last-resort antimicrobials used to treat multidrug-resistant bacterial infections, faces challenges due to emerging plasmid-borne resistance mechanisms, including the enzymatic inactivation of antimicrobials. Here, we investigate and report the co-occurrence of bla and tet(X7) genes in an Acinetobacter towneri isolate from hospital wastewater in the Philippines.

Methods: An A. towneri isolate PT23-B2 was obtained from a hospital wastewater treatment plant in Tacloban, Philippines in 2023. Whole-genome sequencing of PT23-B2 was performed and antimicrobial resistance genes (ARGs), plasmids, and mobile genetic elements were detected using custom sequence databases.

Results: Whole-genome sequencing analysis of A. towneri PT23-B2 resulted in the complete genome sequence consisting of one chromosome and five putative plasmids. One of the five plasmids identified, the 134-kb plasmid named pPT23-B2_1 (of which replicon was classified as R3-T45 or GR31), contained multiple ARGs, including bla and tet(X7). The bla was flanked by ISAba125, and tet(X7) was associated with one IS26 family insertion sequence (IS), indicating probable transpositions into the plasmid via these mobile genetic elements. Antimicrobial susceptibility tests showed that PT23-B2 is resistant to tigecycline, in addition to meropenem.

Conclusions: This is the first report on an environmental bacterial isolate from the Philippines harbouring both carbapenem-resistance gene (bla) and tigecycline-resistance gene [tet(X7)]. This study highlights the potential dissemination of clinically important ARGs, such as bla and tet(X), in environmental reservoirs, necessitating continuous monitoring and urgent intervention strategies.