First report on methicillin-resistant Staphylococcus aureus of Spa type T037, Sequence type 239, SCCmec type III/IIIA in Malaysia

The emergence and global spread of methicillin-resistant Staphylococcus aureus (MRSA) over the past five decades constitutes one of the most serious contemporary challenges to the successful treatment of hospital-acquired infections. The enhanced success of MRSA in acquiring resistance to additional groups of antimicrobial agents renders infections caused by these pathogens very difficult to manage and expensive to treat [1]. The prevalence rate of MRSA varies widely among cities, countries and continents because of the clonal dissemination of locally prevalent MRSA clones. The genotypic characteristics of MRSA strains from 12 Asian countries assessed recently by multi-locus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing identified clonal cluster 5 (CC5) MRSA of SCCmec type II (CC5-MRSA-II) as a prototype clone in Korea and Japan while CC239-MRSA-III (or IIIA) appeared to be the major clone in other Asian countries [2]. The above study did not include isolates from Malaysia, another Asian country where the prevalence of MRSA in several hospitals is over 40% [3], but information on the molecular characteristics and clonal distribution of Malaysian MRSA is still limited. Therefore, the aim of the current study was to determine the SCCmec and sequence types of the predominant clones circulating in a large public hospital in Malaysia.

Thirty-six non-repetitive invasive MRSA strains isolated from different clinical sources (blood, pus, urine and tracheal aspirates) collected from a public hospital in Klang Valley (Malaysia) from September 2006 to February 2007 were examined. Isolates were classified as HA and CA-MRSA based on the date of admission, specimen collection date, the number of previous admissions and hospital exposures, and prolonged hospital stays. All isolates were reconfirmed as MRSA by standard laboratory procedures and subjected to SCCmec and Spa typing [4, 5]. Selected isolates from the dominant Spa types were further typed by MLST [6]. Pulsed field gel electrophoresis (PFGE) typing was performed to define the precise relatedness among the strains [7].

Among the 36 isolates (Fig. 1), 15 (41.6%) and 19 (52.7%) possessed SCCmec type III and IIIA respectively, while 2 isolates (5.5%) were SCCmec type V. The SCCmec V isolates were also Panton-Valentine leukocidin (PVL)-positive as was reported previously [8]. Molecular typing by Spa sequencing and MLST identified t037 and ST 239 belonging to CC8 as the most predominant MRSA, covering 83.3% of the isolates studied. Other Spa and sequence types such as t074, t421, t3103, t127 (ST1) and t657 (ST 772) were found incidentally. Spa t074 and t421 are closely related to t037 and arose from the same Spa ancestor (CC-37), while t657 and t3013 are singletons. Strain relatedness within the hospital as defined by PFGE typing grouped all the isolates from the t037, t074 and t421 into one major cluster at approximately 75% similarity, with t657 and t127 in the sub-cluster at 50% similarity, while t3013 was distantly related (less than 40%) and segregated separately (bottom part of Fig. 1). Although the PFGE pattern showed a 40–100% variation among the strains, no clones specific to clinical source, ward or the period of collection were detected. The combined result of PFGE, Spa, MLST and SCCmec typing clearly shows that ST 239 III (or IIIA)-Spa t037 was predominantly circulating in the hospital during the study period (Fig. 1).

To date, five major pandemic MRSA clones have been reported. These include the Iberian or ST 247-IA clone, the Brazilian or ST 239-IIIA clone, the Hungarian or ST 239-III clone, the New York/Japan or ST 5-II clone, and the paediatric or ST 5-IV clone. Much of the old nomenclature reflects the geographic area in which these MRSA clones were first identified [1]. In Malaysia we have now also identified ST 239, a clone that was first identified in Brazil in 1995 [9] and which was later reported from Hungary in 1997 [10]. Interestingly, the 239 clone disappeared from Hungarian institutions between 1998 and 2003 where it was largely replaced by ST 228-I and ST 5-II [11]. In addition, the ST 239 clone was also identified in Saudi Arabia and Romania [2]. A recent paper from 11 Asian countries reported that ST 239 accounts for at least 90% of the HA-MRSA in the greater Asian region, which comprises over 60% of the world’s population [2].

We identify ST 239-III (or IIIa) as the predominant clone in a single hospital over a 5-month period. Although we analysed a limited number of isolates only, this still indicates that this clone is a major one in Malaysia, which is consistent with the previous reports on the dominance of ST 239 in Asia. However, investigations with a large number of strains from different geographical regions in Malaysia need to be carried out to confirm the predominance of ST 239-III (or IIIa) in Malaysia.