The type VI secretion system in Acinetobacter baumannii clinical isolates and its roles in antimicrobial resistance acquisition

Acinetobacter baumannii is a successful pathogen that can acquire various antibiotic resistance in a short time. However, little is known about how it can evolve from an antibiotic sensitive to a resistant phenotype. In this study, we investigated the roles of the type VI secretion system (T6SS) in the acquisition of antibiotic resistance of A. baumannii. T6SS gene cluster was found to be present in 51 of 77 A. baumannii clinical isolates, of which, it was found in 62% (8/13) of the multiple drug resistant (MDR) isolates, 90% (36/40) of the extensively drug -resistant (XDR) isolates and 26% (6/23) of the antibiotic sensitive isolates. There is a close relationship be-tween the antimicrobial resistance and the presence of T6SS. Besides, T6SS + isolates showed lower biofilm formation activity and higher survival ability in the presence of normal human serum than T6SS-isolates. A. baumannii A152 with complete T6SS can outcompete E.coli effectively and can acquire the antibiotic resistance plasmids released by E.coli. In contrast, the T6SS core gene mutant A152 delta hcp showed significantly decreased ability to acquire antimicrobial resistance plasmids from the prey bacteria. These results suggest that T6SS mediated bacterial competition plays important roles in the antimicrobial resistance of A. baumannii, which points out a new direction for us to study the antimicrobial resistance of A. baumannii.

Automated summary

This study investigated the role of the type VI secretion system (T6SS) in the acquisition of antibiotic resistance in Acinetobacter baumannii. The presence of T6SS was found to be closely related to antimicrobial resistance in clinical isolates. T6SS-positive isolates showed differences in biofilm formation and survival ability in the presence of human serum. Furthermore, A. baumannii with complete T6SS was able to outcompete E.coli and acquire antibiotic resistance plasmids. Mutants lacking the T6SS core gene showed decreased ability to acquire antimicrobial resistance plasmids. These findings suggest that T6SS-mediated bacterial competition plays a significant role in antimicrobial resistance of A. baumannii.