The spread of multi-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), which is mediated by the mecA gene, is a threat in treatment of infectious diseases. MRSA has not been detected in wastewater, but the mecA gene has been detected both in municipal and hospital wastewater. The aim of the study was to determine if mecA, S.aureus and MRSA could be detected in a municipal wastewater treatment plant. Furthermore, we wanted to investigate how the wastewater treatment process affects mecA concentrations and occurrence of S.aureus and MRSA, over time.

Wastewater samples were collected monthly, over one year, at eight sites from the treatment plant Ryaverket, Gothenburg, Sweden. The water samples were centrifuged and DNA was extracted from the pellet using FastDNA® Spin Kit for Soil. Quantification of DNA was preformed using PicoGreen® dsDNA Quantitation Kit. Detection of the S.aureus specific nuc-gene and quantification of the mecA gene was preformed using real-time PCR, while MRSA was detected with the BD GeneOhm™ MRSA Test.

The mecA and S.aureus could be detected throughout the year at all sampling sites. MRSA could also be detected in the treatment plant, but mainly in the early treatment steps. The presence of MRSA was verified through cultivation from inlet water.
The concentration of the mecA gene varied between months and sampling sites, but no obvious seasonal variation could be determined. The treatment process reduces the mecA gene concentrations in most months studied, both when related to water volume and to biomass expressed as amount of DNA.