Decreased susceptibility to zinc chloride is associated with methicillin resistant Staphylococcus aureus CC398 in Danish swine

A total of 31 MRSA and 60 MSSA isolated from different swine farms in Denmark were examined for their susceptibility to zinc chloride, erythromycin, penicillin and tetracycline, as well as their spa-type. mecA positive isolates were examined for their SCCmec type. The isolates were assigned to a CC-type based on their spa-type and supportive multi-locus sequence typing (MLST). No difference in susceptibility to erythromycin, penicillin or tetracycline could be observed between methicillin resistant and susceptible isolates of CC398. Twenty-three (74%) of the MRSA CC398 isolates had reduced susceptibility to ZnCl(2) (MIC 4-12 mM), whereas all MSSA had MICs from 0.5 to 2 mM. Thirty MRSA, including all 23 zinc resistant isolates harboured SCCmec type V. This provides biological evidence to suggest that the use of zinc compounds may be partly implicated in the emergence of some MRSA clones among swine in Denmark.