Natural transformation of Acinetobacter baumannii

Antimicrobial resistance poses a significant global health challenge, contributing to a lack of effective therapeutic agents, especially against Gram-negative bacteria. Resistance dissemination is accelerated by horizontal gene transfer (HGT) mechanisms. Extended-spectrum beta lactamases CTX-M confer resistance to several beta-lactams are usually embedded into plasmids and thought to be mainly disseminated by conjugation. However an increasing number of isolates carry these enzymes in the chromosome, suggesting that they can spread by other means of HGT. In this study, we aimed to test the involvement of natural transformation in the chromosomal acquisition of a blaCTX-M gene. The naturally competent clinical strain Acinetobacter baumannii A118 was transformed with naked DNA from Salmonella enterica serovar Typhimurium Sal25 isolated from swine meat. Whole genome sequencing of the transformant revealed the acquisition of the blaCTX-M-32 as part of a ca. 36 Kb DNA fragment through an ISEc9-mediated transposition evenOur results highlight the importance of natural transformation events in the dissemination of antimicrobial resistance genes and mobile genetic elements between and within species.