Targeted insights into Aeromonas hydrophila biofilms: Surface preferences, resistance mechanisms, and gene expression

This study provides a comprehensive analysis of biofilm formation, antibiotic resistance, motility, and gene expression in four Aeromonas hydrophila strains-ATCC 15467, ATCC 7966, KCTC 2358, and KCTC 11533-on stainless steel (SS), silicon rubber (SR), polyethylene terephthalate (PET), and high-density polyethylene (HDPE) surfaces over 24, 48, 72, and 96 h. Biofilm formation peaked at 72 h, with ATCC 7966 demonstrating the highest biofilm density on PET (6.50 ± 0.08 log CFU/cm²), underscoring PET's role as a favorable substrate for biofilm development. In contrast, HDPE consistently exhibited the lowest biofilm levels, reflecting its potential as a biofilm-resistant material. Antibiotic susceptibility profiling revealed multidrug resistance (MDR) in ATCC 15467 and KCTC 11533 (MARI = 0.80), particularly against beta-lactams, aminoglycosides, and fluoroquinolones while ATCC 7966 and KCTC 2358 displayed moderate resistance. Motility assays highlighted strain-specific capabilities, with KCTC 11533 exhibiting the highest swimming motility (76.0 ± 6.6 mm) and KCTC 2358 excelling in swarming (47.7 ± 3.5 mm). Genetic analysis confirmed the presence of luxS and ahyR in all strains, while csgA was exclusive to ATCC 7966, correlating with its superior biofilm formation. Confocal microscopy revealed biofilm maturation dynamics, with red fluorescence indicating cell death and aging at 96 h, while SEM images captured intricate surface-specific biofilm architectures. These findings elucidate the critical interplay between strain characteristics, surface properties, and incubation time, providing a foundation for developing targeted strategies to control A. hydrophila biofilms in food processing environments.