Antimicrobials affect the production and characteristics of outer membrane vesicles of Acinetobacter baumannii

Abstract:

[Background] Antimicrobial resistance poses a huge threat to global health and economic development. Tigecycline is one of the important drugs for treating severe infections caused by multidrug-resistant Enterobacteriaceae. However, the mobile resistance gene tet(X3), which could mediate high-level tigecycline resistance, was discovered in 2019. Outer membrane vesicles have been recognized as a new route for horizontal gene transfer, while little is known about the role of outer membrane vesicles in the disseminating of tet(X3). [Objective] To investigate the effects of different antimicrobials on the production and characteristics of outer membrane vesicles of tet(X3)-positive tigecycline-resistant Acinetobacter baumannii strain 34AB. [Methods] The antimicrobial susceptibility was determined by the broth micro-dilution method. The bacterial outer membrane vesicles were extracted by ultracentrifugation. The protein concentration of the outer membrane vesicles was determined by the BCA method, and the size and potential tested by Zeta-sizer nano-ZS. The copy number of tet(X3) within the outer membrane vesicles was determined by RT-qPCR. [Results] Compared with the control group without antibiotic treatment [(0.64±0.04) mg/mL], antimicrobials at 1/2 MIC or 1/4 MIC increased the production of outer membrane vesicles, with the effects of ceftazidime [1/2 MIC, (2.83±0.57) mg/mL; 1/4 MIC, (2.38±0.29) mg/mL] and meropenem [1/2 MIC, (2.19±0.11) mg/mL; 1/4 MIC, (1.96±0.37) mg/mL] being the most significant (P<0.01). Meanwhile, the antimicrobial treatments decreased the size and potential of outer membrane vesicles and increased the copy number of tet(X3) (2.80×10⁴-2.63×10⁷copies/μL). [Conclusion] The clinical application of antimicrobials may increase the production and the antimicrobial resistance gene abundance of outer membrane vesicles, thereby increasing the risk of them as vectors for disseminating of antimicrobial resistance genes.

Key words:Acinetobacter baumannii;outer membrane vesicle;tigecycline;antimicrobial resistance;tet(X3)