Survival of environmental and clinical strains of methicillin-resistant Staphylococcus aureus [MRSA] in marine and fresh waters

Recent studies have found variable levels of methicillin-resistant Staphylococcus aureus MRSA] in marine water from temperate and warmer climates suggesting that temperature may play a role in survival of MRSA in the environment. The aim of the study was to compare the survival of clinical and environmental MRSA and MSSA strains in fresh and marine water incubated at 13 °C and 20 °C over 14 days. Seven different MRSA strains and the MSSA ATCC 25923 were tested. Individual strains were diluted in sterile saline to a 0.5 McFarland standard (10⁸ cfu/ml), serially diluted in duplicate to a final concentration of 10⁵ cfu/ml in pooled filter-sterilized marine or fresh water and incubated at 13 °C or 20 °C in the dark. The results of this study found that temperature and salinity are important factors in MRSA and MSSA survival; the decay rate was ∼28% higher at 20 °C versus 13 °C and ∼34-44% higher in fresh water versus marine water. There was no statistical difference between environmental and clinical MRSA strain survival P = 0.138]. The study found that MRSA/MSSA survival was significantly longer in marine water at 13 °C typical of the Pacific Northwest, which may have important implications for recreational beach visitors in colder climates.