Non-methicillin resistant bacteria were not found to produce these toxins. Although PSM toxins are produced in all methicillin-resistant Staphylococcus aureus strains, the more virulent CA-MRSA strains are typically associated with higher production. Genetic analysis demonstrated that the PSM-alpha protein, product of the psm-alpha gene cluster, was associated with enhanced virulence and enhanced destruction of white blood cells, presumably the key to the higher infectivity. However, expression of the psm-alpha genes appeared to vary, dependent upon unknown factors specific to each particular infection.
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