<i>Aeromonas hydrophila</i> biofilm, exoprotease, and quorum sensing responses to co-cultivation with diverse foodborne pathogens and food spoilage bacteria on crab surfaces

The effects of dual species interactions on biofilm formation by <i>Aeromonas hydrophila</i> in the presence of <i>Pseudomonas aeruginosa</i>, <i>Pseudomonas fluorescens</i>, <i>Pectobacterium carotovorum</i>, <i>Salmonella</i> Typhimurium, and <i>Listeria monocytogenes</i> were examined. High-performance liquid chromatography and liquid-chromatography-mass spectrometry were performed to identify <i>N</i>-acyl homoserine lactone (AHL) molecules secreted by monocultures and dual cultures grown in crab broth. Field emission scanning electron microscopy was performed to observe attachment and biofilm formation. <i>P. aeruginosa</i> and <i>P. fluorescens</i> inhibited biofilm formation by <i>A. hydrophila</i> on the crab surface, without affecting their own biofilm-forming abilities. Dual biofilms of <i>S.</i> Typhimurium, <i>L. monocytogenes</i>, or <i>P. carotovorum</i> did not affect <i>A. hydrophila</i> biofilm formation. Exoprotease, AHL, and AI-2 levels were significantly reduced in dual cultures of <i>P. aeruginosa</i> and <i>P. fluorescens</i> with <i>A. hydrophila</i>, supporting the relationship between quorum sensing and biofilm formation. Dual-species biofilms were studied in their natural environment and in the laboratory.