Pseudomonas aeruginosa affects Acinetobacter baumannii's growth, gene expression and antibiotic resistance in in vitro co-culture system.

Pseudomonas aeruginosa and Acinetobacter baumannii are opportunistic pathogens co-isolated frequently in the same infection sites. In this study, we aimed to elucidate the interaction between P. aeruginosa and A. baumannii in in vitro co-culture system. Growth analysis showed that P. aeruginosa PA01 unilaterally exerts a negative effect on the growth of A. baumannii SK005. A. baumannii alone exhibited an altered transcriptome pattern, especially in the genes for metabolic pathways. Strong upregulation of genes in iron acquisition systems (acinetobactin, baumannoferrin, 2,3-dihydroxybenzoic acid synthesis cluster, and Feo iron transport system) and downregulation of iron-storage genes (bacterioferritin) were the most prominent changes. In terms of antibiotic resistance, we observed the downregulation of the fosfomycin resistance gene fosB. Strikingly, the phenotypic analysis demonstrated that A. baumannii in co-culture is more vulnerable to fosfomycin than in monoculture conditions, while it is more resistant to cefoxitin and imipenem. This study broadens our understanding of microbial ecology in co-infection settings by highlighting the fact that mixed pathogens do not always undergo interaction to a mutually equivalent extent.