The role of type VI secretion system genes in antibiotic resistance and virulence in clinical isolates.

Introduction: The type VI secretion system (T6SS) is a crucial virulence factor in the nosocomial pathogen . However, its association with drug resistance is less well known. Notably, the roles that different T6SS components play in the process of antimicrobial resistance, as well as in virulence, have not been systematically revealed.

Methods: The importance of three representative T6SS core genes involved in the drug resistance and virulence of , namely, , (), and was elucidated.

Results: A higher ratio of the three core genes was detected in drug-resistant strains than in susceptible strains among our 114 clinical isolates. Upon deletion of in AB795639, increased antimicrobial resistance to cefuroxime and ceftriaxone was observed, alongside reduced resistance to gentamicin. The Δ mutant showed decreased resistance to ciprofloxacin, norfloxacin, ofloxacin, tetracycline, and doxycycline, but increased resistance to tobramycin and streptomycin. The -lacking mutant showed an increased sensitivity to ofloxacin, polymyxin B, and furazolidone. In addition, a significant reduction in biofilm formation was observed only with the Δ mutant. Moreover, the Δ strain, followed by the Δ mutant, showed decreased survival in human serum, with attenuated competition with and impaired lethality in .

Discussion: The above results suggest that T6SS plays an important role, participating in the antibiotic resistance of , especially in terms of intrinsic resistance. Meanwhile, and contribute to bacterial virulence to a greater degree, with tssM being associated with greater importance.