Colistin Affects Biofilm Formation and the Electrokinetic Potential Profile in Environmental Pseudomonas spp.: Comparative Genomics and Phenotypic Analysis

Colistin is a last-resort antibiotic used to treat infections caused by multidrug-resistant Gram-negative bacteria. Although genetic determinants of resistance have been extensively studied, the functional and physiological responses of bacteria to colistin exposure remain incompletely understood. In this study, environmental Pseudomonas spp. isolates revealing distinct patterns of genomic similarity in the ANI-based analysis were studied to investigate phenotypic and genomic responses associated with colistin exposure. Pseudomonas spp. exhibited diverse colistin susceptibility profiles, reflecting substantial heterogeneity among the analyzed isolates. Sub-inhibitory concentrations of colistin significantly modulated biofilm formation in a strain-dependent manner, resulting in both enhancement and inhibition of its synthesis. Electrokinetic analyses revealed pronounced alterations in cell surface charge, with colistin-susceptible strains showing increased negative surface charge, whereas colistin-resistant isolates exhibited more limited and concentration-dependent responses. Whole-genome sequencing identified a broad repertoire of genes potentially associated with antimicrobial resistance, including those involved in efflux systems, membrane modification, and heavy-metal resistance. These findings indicate that colistin induces complex, strain-specific physiological responses that extend beyond its antimicrobial activity and involve dynamic remodeling of the bacterial cell envelope and associated surface properties.