Pathogens in the bay: environmental Staphylococcus saprophyticus strains mirror clinical counterparts in virulence, biofilm formation, antimicrobial resistance, pathogenicity, and phage susceptibility

Abstract Staphylococcus saprophyticus is a leading cause of urinary tract infections, yet little is known about its environmental reservoirs and traits outside clinical settings. This study aimed to compare clinical and environmental S. saprophyticus strains isolated from a polluted coastal ecosystem in Brazil, assessing their virulence-associated traits, antimicrobial resistance, biofilm formation, and susceptibility to bacteriophages. Forty strains (20 clinical, 20 environmental) were characterized using GTG 5 -PCR, virulence gene screening, antibiotic susceptibility testing, biofilm assays, exposure to sub-inhibitory concentrations of ciprofloxacin, Tenebrio molitor infection model, and phage activity tests. Genetic fingerprinting and virulence gene profiles revealed a high degree of similarity between environmental and clinical isolates, indicating the presence of shared virulence-associated determinants. Environmental strains exhibited resistance to multiple antibiotics and showed biofilm formation and larval survival patterns comparable to those observed for clinical isolates. Exposure to sub-inhibitory concentrations of ciprofloxacin increased biofilm formation in several strains. Bacteriophage CSF, originally isolated from swine farm effluent, displayed lytic and antibiofilm activity against a substantial proportion of the isolates. These findings highlight the presence of clinically relevant traits among environmental S. saprophyticus strains and underscore the importance of continued microbiological surveillance in anthropized aquatic environments.