EXTENSIVE GENETIC DIVERSITY IDENTIFIED AMONG SPORADIC METHICILLIN-RESISTANT Staphylococcus aureus ISOLATES RECOVERED IN IRISH HOSPITALS BETWEEN 2000-2012

Abstract

Clonal replacement of predominant nosocomial methicillin-resistant Staphylococcus aureus (MRSA) strains has occurred several times in Ireland during the last four decades. However, little is known about sporadically-occurring MRSA in Irish hospitals or in other countries. Eighty-eight representative pvl-negative sporadic MRSA isolates recovered in Irish hospitals between 2000-2012 were investigated. These yielded unusual pulsed-field gel electrophoresis and antibiogram-resistogram typing patterns distinct from those of the predominant nosocomial MRSA clone, ST22-MRSA-IV, during the study period. Isolates were characterized by spa typing and DNA microarray profiling for multilocus sequence type (MLST) clonal complex (CC) and/or sequence type (ST) and SCCmec type assignment, and for detection of virulence and antimicrobial resistance genes. Conventional PCR-based SCCmec subtyping was undertaken when necessary. Extensive diversity was detected including 38 spa types, 13 MLST-CCs including 18 STs among 62 isolates assigned to STs and 25 SCCmec types including two possible novel SCCmec elements and seven possible novel SCCmec subtypes. Fifty-four MLST-spa-SCCmec type combinations were identifed. Overall 68.5% of isolates were assigned to nosocomial lineages with ST8-t190-MRSA-IID/IIE +/- SCCM1 predominating (17.4%) followed by CC779/ST779-t878-MRSA-?SCCmec-SCC-SCCCRISPR (7.6%) and CC22/ST22-t032-MRSA-IVh (5.4%). Community-associated clones including CC1-t127/t386/t2279-MRSA-IV, CC59-t216-MRSA-V, CC8-t008-MRSA-IVa, CC5-t002/t242-MRSA-IV/V and putative animal-associated clones including CC130-t12399-MRSA-XI, ST8-t064-MRSA-IVa, ST398-t011-MRSA-IVa and CC6-t701-MRSA-V were also identified. In total, 53.3% and 47.8% of isolates harbored resistance genes to two or more classes of antimicrobial agents and two or more mobile genetic element-encoded virulence-associated factors, respectively. Effective ongoing surveillance of sporadic nosocomial MRSA is warranted for early detection of emerging clones and reservoirs of virulence, resistance and SCCmec genes.