Comparative Molecular Characterization of Resistance and Virulence in Staphylococcus aureus from Sewage Effluents and Impacted Marine Outfalls

Environmental surveillance is important to monitor and mitigate antimicrobial resistance (AMR). In this context, sewage and its marine outfalls remain a hot spot for spreading AMR among pathogens. This study investigated the presence of drug-resistant Staphylococcus aureus in sewage effluent and marine sewage outfalls in Saudi Arabia. Water samples were collected from Jeddah's southern and central marine outfalls and non-impacted sites. The isolates (n = 120) were identified through biochemical tests and MALDI-TOF. Resistance to antibiotics in the isolates was initially screened through phenotypic methods. Species-specific markers and antibiotic resistance genes (ARGs) were amplified through PCR. The presence of ARGs was also quantified in the isolates and in the environment through qPCR. The data indicated a higher prevalence of methicillin-resistant S. aureus (MRSA) in sewage effluent (63.3%) compared to marine water (50%). Sewage-borne MRSA exhibited higher resistance to various antibiotics. PCR detection confirmed the presence of mecA in MRSA isolates. Virulence genes encoding microbial surface components and recognizing adhesive matrix molecules (MSCRAMMs) were more prevalent in sewage isolates. Particularly, genes responsible for biofilm formation were more prevalent in the isolates from sewage samples. qPCR revealed a higher abundance of mecA, fnbB and bbp in sewage-derived isolates. Statistical analysis confirmed the strong influence of the sewage environment on the prevalence of drug-resistant isolates. Screening of environmental DNA further validated sewage as a reservoir of resistance and virulence determinants. These findings highlight the role of sewage outfalls in disseminating ARGs and virulent S. aureus strains, emphasizing the need to improve wastewater treatment and environmental surveillance strategies.