The effect of culture conditions on the in-vitro adherence of methicillin-resistant Staphylococcus aureus

Methicillin-resistant isolates of Staphylococcus aureus (MRSA) were divided on the basis of their epidemiologic behaviour into two subgroups, epidemic MRSA (EMRSA) and sporadic MRSA (SMRSA) strains. An existing adherence assay was modified to determine differences in adherence properties between these two groups of MRSA, and the influence of culture conditions on the adherence of SMRSA and EMRSA strains to plastic, human collagen I (HuCol I) and pharyngeal carcinoma Detroit 562 cells (D562) was determined. In-vitro parameters, such as culture medium, growth temperature and growth phase of the bacterium, influenced the adherence of MRSA strains to plastic significantly. Even more pronounced differences in adherence due to changes in growth conditions and growth phase of the bacteria were found for the adherence of MRSA strains to HuCol I. Growth phase had a significant effect on the adherence of MRSA strains to the pharyngeal carcinoma cells D562. However, the study did not find conditions which made it possible to distinguish EMRSA from SMRSA strains. These data show that extrapolation of in-vitro data concerning adherence of MRSA strains to in-vivo conditions should be treated with caution.