In vitro virulence activity of Pseudomonas aeruginosa, enhanced by either Acinetobacter baumannii or Enterococcus faecium through the polymicrobial interactions.

Microbes within an infection impact neighbors' pathogenicity. This study aimed to address in vitro virulence activity of Pseudomonas aeruginosa under the binary interaction with Acinetobacter baumannii or Enterococcus faecium, co-isolated from two chronic wound infections. The biofilm formation of Pseudomonas was enhanced 1.5- and 1.4-fold when it was simultaneously cultured with Acinetobacter and Enterococcus, respectively. Pseudomonas motility was increased by 1.9- and 1.5-fold (swimming), 3.6- and 1.9-fold (swarming), and 1.5- and 1.5-fold (twitching) in the dual cultures with Acinetobacter and Enterococcus, respectively. The synergistic hemolysis activity of Pseudomonas was observed with the heat-killed Acinetobacter and Enterococcus cells. The minimum inhibitory concentration of ciprofloxacin against Pseudomonas was increased from (μg mL -1 ) 25 to 400 in the individual and mixed cultures, respectively. The pyocyanin production by Pseudomonas in the single and mixed cultures with Acinetobacter and Enterococcus was (μg/mL) 1.8, 2.3, and 2.9, respectively. The expression of lasI, rhlI, and pqsR genes was up-regulated by 1.0-, 1.9-, and 16.3-fold, and 4.9-, 1.0-, and 9.3-fold when Pseudomonas was incubated with Acinetobacter and Enterococcus, respectively. Considering the entire community instead of a single pathogen may lead to a more effective therapeutic design for persistent infections caused by Pseudomonas.