Prevalence, antibiogram and molecular characterization of methicillin-resistant staphylococcus aureus recovered from treated wastewater effluent and receiving surface water.
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Inadequately treated wastewater effluent serves as a reservoir of potentially pathogenic bacteria and contributes to the spread of these organisms in the environment, including Staphylococcus aureus (S. aureus), a faecal bacterium known to cause pneumonia, septicaemia and skin infections in humans. The presence of S. aureus in water has become problematic as it has been shown to exhibit resistance towards β-lactam antibiotics commonly used to treat infections, including methicillin, leading to the emergence of methicillin-resistant S. aureus (MRSA). The current study aimed to determine the prevalence of MRSA and mecA (known to induce methicillin resistance) in the influent, treated effluent and receiving surface rivers of two wastewater treatment plants (WWTPs) in Durban. The study also evaluated the antibiogram and virulence gene profiles of MRSA isolates recovered from the treated effluent and receiving surface water using the Kirby-Bauer disc diffusion and PCR assays. Genetic fingerprinting was carried out to determine the phylogenetic relationship between isolates with selected antibiogram profiles. The prevalence of MRSA in WWTP1 ranged from 11.45-85.63% (influent), 16.28-39.36% (before chlorination), 2.16-5.07% (after chlorination), 1.06-7.24% (downstream) and 4.95-14.09% (upstream). In WWTP2, the prevalence of MRSA for the influent ranged from 48.25-86.18%, before chlorination; 23.73-93.75%, after chlorination; 4.28-48.82%, downstream; 1.74-19.31% and upstream; 5.90-28.78%. Correlation studies of selected physico-chemical parameters to the prevalence of MRSA was carried out. The real-time PCR assay showed a reduction in the concentration of mecA from the influent to the treated effluent in both WWTPs. The highest resistance was observed towards lincomycin (100%), followed by oxacillin (98.75%), cefoxitin and penicillin (97.50%) and ampicillin (96.25%). Additionally, 72.50%, 66.25%, 52.50%, 40% and 33.75% of the isolates showed resistance against cefozolin, azithromycin, amoxicillin/clavulanic acid, erythromycin and vancomycin, respectively. The following antibiotic resistance genes were detected in resistant isolates: aac(6ꞌ)/aph(2ꞌꞌ) in 56.25%, ermC in 62.50%, msrA in 22.50% and blaZ and tetK in 70%. The virulence genes hla and sea were detected in 57.50% of the isolates, hld in 1.25% and the lukS P/V gene was not detected. Thirteen pulsotypes v (designated A-M) was generated for selected isolates using pulse field gel electrophoresis, correlating them to their respective antibiograms. The study revealed a lower prevalence of MRSA and concentration of mecA in the treated effluent as compared to the influent of both WWTPs. It also revealed that these multi-drug resistant strains, isolated from the treated effluent and receiving surface waters, are potentially pathogenic and could contribute to the spread of disease in the environment. Hence, the need for more stringent monitoring and evaluation of treatment performance of the WWTPs.