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

<i>Pseudomonas aeruginosa</i> and <i>Acinetobacter baumannii</i> are opportunistic pathogens co-isolated frequently in the same infection sites. In this study, we aimed to elucidate the interaction between <i>P. aeruginosa</i> and <i>A. baumannii</i> in <i>in vitro</i> co-culture system. Growth analysis showed that <i>P. aeruginosa</i> PA01 unilaterally exerts a negative effect on the growth of <i>A. baumannii</i> SK005. <i>A. baumannii</i> 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 <i>fosB</i>. Strikingly, the phenotypic analysis demonstrated that <i>A. baumannii</i> 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.