Abstract
In Australia the PVL - positive ST93-IV [2B], colloquially known as “Queensland CA-MRSA” has become the dominant CA-MRSA clone. First described in the early 2000s, ST93-IV [2B] is associated with skin and severe invasive infections including necrotizing pneumonia. A singleton by multilocus sequence typing (MLST) eBURST analysis ST93 is distinct from other S aureus clones. To determine if the increased prevalence of ST93-IV [2B] is due to the widespread transmission of a single strain of ST93-IV [2B] the genetic relatedness of 58 S. aureus ST93 isolated throughout Australia over an extended period were studied in detail using a variety of molecular methods including pulsed-field gel electrophoresis, spa typing, MLST, microarray DNA, SCCmec typing and dru typing. Identification of the phage harbouring the lukS-PV/lukF-PV Panton Valentine leucocidin genes, detection of allelic variations in lukS-PV/lukF-PV, and quantification of LukF-PV expression was also performed. Although ST93-IV [2B] is known to have an apparent enhanced clinical virulence, the isolates harboured few known virulence determinants. All PVL-positive isolates carried the PVL-encoding phage ΦSa2USA and the lukS-PV/lukF-PV genes had the same R variant SNP profile. The isolates produced similar expression levels of LukF-PV. Although multiple rearrangements of the spa sequence have occurred, the core genome in ST93 is very stable. The emergence of ST93-MRSA is due to independent acquisitions of different dru-defined type IV and type V SCCmec elements in several spa-defined ST93-MSSA backgrounds. Rearrangement of the spa sequence in ST93-MRSA has subsequently occurred in some of these strains. Although multiple ST93-MRSA strains were characterised, little genetic diversity was identified for most isolates, with PVL-positive ST93-IVa [2B]-t202-dt10 predominant across Australia. Whether ST93-IVa [2B] t202-dt10 arose from one PVL-positive ST93-MSSA-t202, or by independent acquisitions of SCCmec-IVa [2B]-dt10 into multiple PVL-positive ST93-MSSA-t202 strains is not known.
Highlights
The community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) worldwide epidemic is polyclonal, several well characterized clones predominate in different regions of the world: Sequence type (ST) 8-IV [2B] (USA300) and ST1-IV [2B] (USA400) in North America [1,2]; ST80-IV [2B] (European clone) in Europe [3], North Africa [4] and the Middle East [5]; ST59-V [5C2&5] (Taiwan clone) in Taiwan [6], ST30-IV [2B] (South West Pacific [SWP] CA-MRSA) in the Western Pacific [7,8] and ST772-MRSA-V [5C2] (Bengal Bay clone) in India and Bangladesh [9]
The vertical and horizontal transmission of SCCmec elements into S. aureus has occurred on multiple occasions in the Australian community only a small number of clones have successfully found an ecological niche to predominate over other CA-MRSA clones [40]
We have shown the emergence of ST93-MRSA has been due to independent acquisitions of different dru-defined type IV and type V SCCmec elements in several spa-defined ST93MSSA backgrounds
Summary
The community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) worldwide epidemic is polyclonal, several well characterized clones predominate in different regions of the world: Sequence type (ST) 8-IV [2B] (USA300) and ST1-IV [2B] (USA400) in North America [1,2]; ST80-IV [2B] (European clone) in Europe [3], North Africa [4] and the Middle East [5]; ST59-V [5C2&5] (Taiwan clone) in Taiwan [6], ST30-IV [2B] (South West Pacific [SWP] CA-MRSA) in the Western Pacific [7,8] and ST772-MRSA-V [5C2] (Bengal Bay clone) in India and Bangladesh [9]. First described in the early 2000s, ST93 is a singleton by MLST eBURST analysis and is distinct from other S aureus clones [12]
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