Predominance and Emergence of Clones of Hospital-Acquired Methicillin-Resistant Staphylococcus aureus in Malaysia

We define the epidemiology of predominant and sporadic methicillin-resistant Staphylococcus aureus (MRSA) strains in a central teaching and referral hospital in Kuala Lumpur, Malaysia. This is done on the basis of spa sequencing, multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing, and virulence gene profiling. During the period of study, the MRSA prevalence was 44.1%, and 389 MRSA strains were included. The prevalence of MRSA was found to be significantly higher in the patients of Indian ethnicity (P < 0.001). The majority (92.5%) of the isolates belonged to ST-239, spa type t037, and possessed the type III or IIIA SCCmec. The arginine catabolic mobile element (ACME) arcA gene was detected in three (1.05%) ST-239 isolates. We report the first identification of ACME arcA gene-positive ST-239. Apart from this predominant clone, six (1.5%) isolates of ST-22, with two related spa types (t032 and t4184) and a singleton (t3213), carrying type IVh SCCmec, were detected for the first time in Asia. A limited number of community-acquired (CA) MRSA strains were also detected. These included ST-188/t189 (2.1%), ST-1/t127 (2.3%), and ST-7/t091 (1%). Panton-Valentin leukocidin (PVL) was detected in all ST-1 and ST-188 strains and in 0.7% of the ST-239 isolates. The majority of the isolates carried agr I, except that ST-1 strains were agr III positive. Virulence genes seg and sei were seen only among ST-22 isolates. In conclusion, current results revealed the predominance of ST-239-SCCmec III/IIIA and the penetration of ST-22 with different virulence gene profiles. The emergence in Malaysia of novel clones of known epidemic and pathogenic potential should be taken seriously.Methicillin-resistant Staphylococcus aureus (MRSA) is an established human pathogen that causes both health care-associated (HA) and community-acquired (CA) infections. Modern MRSA has evolved from several successful clonal lineages of methicillin-susceptible S. aureus strains via acquisition of a mobile genetic element called staphylococcal cassette chromosome mec (SCCmec). This element contains the mecA gene, which encodes penicillin-binding protein 2′ (PBP2′) with significantly reduced affinity for β-lactams (36).Increased emergence of multidrug resistance among MRSA strains has become a major concern in the hospital environment, as it invokes a tremendous financial burden and enhanced morbidity and mortality due to hard-to-treat systemic infections (7). Genotyping data from large international studies have shown that a limited number of major clones of MRSA display an enhanced propensity to spread and cause opportunistic human infections in various parts of the world (5, 13, 33). MRSA was introduced into Malaysia in the early 1970s (26), and a review of the records of the microbiology laboratories of all state hospitals in Malaysia showed that the proportion of MRSA isolates from S. aureus-infected individuals had been approximately 21% throughout the last few years.Phenotypic MRSA typing methods are not suited to detailed epidemiological surveillance (20, 40). Several superior molecular typing methods can be used for supporting infection control and for tracing the nosocomial sources and transmission routes of bacterial pathogens. Among these methods, multilocus sequence typing (MLST) has recently been proven to be the best for long-term global epidemiological and bacterial population genetics studies. It is a discriminatory genotypic method where isolates are typed by sequencing variable regions of housekeeping genes. A combination of alleles from the seven loci forms a sequence type (ST). Similar STs are grouped into clonal complexes (13). spa typing has been shown to be as discriminatory as the current gold standard method, pulsed-field gel electrophoresis (PFGE) (10). spa types can be determined via amplification and sequencing of the X region of the protein A gene (spa), which contains polymorphic direct repeats. StaphType (version 1.4; Ridom GmbH, Würzburg, Germany) provides a software tool enabling straightforward sequence analysis and designation of spa types by synchronization via a central server (42). spa typing is useful in analyzing hospital outbreaks and in identifying genetic changes that occur over a relatively short time span (14, 43). Molecular typing data on HA MRSA isolates in Malaysia are sparse in comparison with those on strains deriving from Europe, the United States, or Japan. This is notwithstanding the steadily increasing but already high rates of MRSA infections in Malaysia (38). Pilot data hinted at the predominance of a single MRSA genotype in Malaysia. This is similar to the situation in many other Asian countries (1, 23, 31).For the present study, clinical MRSA isolates associated with various infections were collected from the largest public tertiary referral hospital in Kuala Lumpur, the capital of Malaysia. The epidemiology of MRSA in this hospital (HKL) will most likely reflect the nation''s epidemiology as it is the major government referral hospital for patients from all states in Malaysia. Each year at least 1 million people (∼3.8% of the total Malaysian population) are treated here. HKL records an annual MRSA prevalence over 40%. Many of these MRSA strains are multidrug resistant. Additional epidemiological studies are clearly warranted in order to increase the insight into the dynamics of MRSA epidemiology in Malaysia.The aims of the present study were to characterize the current Malaysian MRSA isolates and determine their molecular epidemiology by MLST, spa typing, SCCmec typing, and virulence gene profiling.