Methicillin-resistant Staphylococcus aureus (MRSA) in municipal wastewater: an uncharted threat?

The aims of this study were to: (i) To cultivate methicillin-resistant Staphylococcus aureus (MRSA) from a full-scale wastewater treatment plant (WWTP), (ii) To characterise the indigenous MRSA-flora, (iii) To investigate how the treatment process affects clonal distribution and (iv)To examine the genetic relation between MRSA from waste water and clinical MRSA. Waste water samples were collected during 2 months at four key sites in the WWTP. MRSA isolates were characterised using spa typing, antibiograms, SSCmec typing and detection of Panton–Valentine leukocidin (PVL). MRSA could be isolated on all sampling occasions, but only from inlet and activated sludge. The number of isolates and diversity of MRSA were reduced by the treatment process, but there are indications that the process was selected for strains with more extensive antibiotic resistance and PVL+ strains. The waste water MRSA-flora had a close genetic relationship to clinical isolates, most likely reflecting carriage in the community. This study shows that MRSA survives in waste water and that the WWTP may be a potential reservoir for MRSA. J Appl Microbiol. 2010;108:1244–51.