Selective pressure governs the composition, antibiotic, and heavy metal resistance profiles of Aeromonas spp. isolated from Ba River in Northwest China.

The selective pressure of the living surroundings is a key factor in the development of resistance profiles in pathogenic bacteria such as Aeromonas spp. In this study, Aeromonas species were isolated from the Ba River, and their composition, resistance profiles to antibiotics, and heavy metals (HMs) were investigated. The discovery revealed that selective pressure altered the diversity of Aeromonas spp., with Aeromonas veronii being more adaptable to contaminated waters. Long-term exposure to antibiotics or HMs exerts persistent selective pressure on Aeromonas species, leading to the increase in multiple antibiotic resistance (MAR) index and multidrug-resistant (MDR) strains. Furthermore, HMs could drive the co-selection of antibiotic resistance via co-resistance or cross-resistance. bla, bla, bla, sul1, czcA, mexA, and mexF were detected at high frequencies in Aeromonas species. Among these resistance phenotypes conferred genes, bla may be intrinsic in the genome of Aeromonas spp., while mexA and mexF may have been acquired from surrounding environments owing to selective pressure. Resistance genes evolved as a consequence of selective pressure and have been shown to be positively correlated with their prevalence. Our study suggests that the selective pressure of living surroundings significantly contributes to the composition and resistance profiles of Aeromonas spp. in the riverine ecosystem.