A potential diagnostic problem: The Newly Emerging mecC Methicillin-Resistant Staphylococcus aureus strains

Background: Methicillin-resistant S. aureus (MRSA) has been known for just over 50 years, and it poses a serious problem for infection prevention and control and antibiotic treatment globally. In MRSA, resistance against almost all beta-lactam compounds in clinical use is caused by the expression of an alternate penicillinbinding protein (PBP2a) that is encoded by the mecA gene. Objective: The report of homologue, designated mecC gene conferring beta-lactam resistance in Staphylococcus aureus poses diagnostic problems with the potential to be misdiagnosed as methicillin-sensitive S. aureus, with important potential consequences for individual patients and for the surveillance of MRSA. Methods: A wide-ranging search of electronic bibliographic databases was performed on mecC-positive Staphylococcus aureus (ST130-MRSA-XI) and the lesions related to the infection in two diseased free-ranging European hedgehogs (Erinaceus europaeus). Results: This gene, mecC, is situated on a SCCmec XI element that has to date been identified in clonal complexes 49, 130, 425, 599 and 1943. Some of the currently known isolates have been identified from animals. This, and observations of mecA alleles that do not confer beta-lactam resistance, indicate that mec genes might have a reservoir in Staphylococcus species from animals. Conclusion: This recently recognised form of MRSA can colonise and cause disease in humans and a wide range of other host species. Although mecC MRSA are currently rare, and have only been reported in Europe to date, they present a potential diagnostic problem where there is reliance on mecA or PBP2a/2′ detection for MRSA diagnosis, and their emergence raises a several opportunities for future research.