Molecular typing of Methicillin-resistant and Methicillin-susceptible Staphylococcus aureus and Coagulase-negative staphylococci recovered in Irish hospitals and characterisation of SCCmec and SCCmec-containing composite islands

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) are a major cause of infections in animals and humans. The methicillin resistance gene mecA is located on a mobile genetic element termed the staphylococcal cassette chromosome mec (SCC/nec). Composite islands (CIs) consisting of two or more SCCmec, SCC or SCC-like elements also occur in MRSA and characterisation of these is essential for accurate typing and tracking of MRSA. Coagulase-negative staphylococci (CoNS) are thought to be a reservoir for SCCmec and other genes in S. aureus. CoNS and methicillin-susceptible S. aureus (MSSA) are leading causes of healthcare-associated infections (HCAIs), but detailed molecular characterisation of both is lacking from Ireland. CoNS often harbour the arginine catabolic mobile element (ACME) that enhances survival on skin. Over the last decade one highly-clonal MRSA lineage, ST22-MRSA-IV, has predominated making tracking of MRSA in Irish hospitals very difficult. The high-throughput StaphyType DNA microarray offers an alternative typing method for S. aureus by assigning isolates to a multilocus sequence type (MLST) and/or clonal complex (CC) and also detects a wide range of virulence, resistance and SCCmec/SCC genes. Combining microarray profiling and spa typing has shown potential for enhancing discrimination of ST22-MRSA-IV isolates and for detecting SCCmec, resistance genes and ACME in CoNS.