Antibiotic resistant Staphylococcus aureus in hospital wastewaters and sewage treatment plants with special reference to methicillin-resistant Staphylococcus aureus (MRSA)

Aims To investigate the presence of methicillin-resistant Staphylococcus aureus (MRSA) in untreated hospital wastewaters (UHWW), their transmission into the receiving sewage treatment plant (STP) and survival through the STP treatment. Methods and Results Over eight consecutive weeks of sampling, we isolated 224 Staph. aureus strains from UHWW-1, UHWW-2 and its receiving STP inlet (SI) and post-treatment outlet (SO). These strains were typed using the PhP typing method and RAPD-PCR and tested for their antibiotic resistance patterns. Resistance to cefoxitin and the presence of mecA gene identified MRSA isolates. In all, 11 common (C) and 156 single (S) PhP-RAPD types were found among isolates, with two multidrug resistant (MDR) C-types found in H2, SI and SO. These C-type strains also showed resistance to cefoxitin and vancomycin. The mean number of antibiotics to which the strains from UHWW were resistant (5.14 +/- 2) was significantly higher than the STP isolates (2.9 +/- 1.9) (P < 0.0001). Among the 131 (68%) MRSA strains, 24 were also vancomycin resistant. MDR strains (including MRSA) were more prevalent in hospital wastewaters than in the STP. Conclusion This study provides evidence of the survival of MRSA strains in UHWWs and their transit to the STP and then through to the final treated effluent and chlorination stage. Significance and Impact of the Study This preliminary study identifies the need to further investigate the load of MRSA in hospitals' wastewaters and possible their survival in STPs. From a public health point of view, this potential route of hospital MRSA dissemination is of great importance.