Predominance and emergence of clones of hospital-acquired methicillin-resistant Staphylococcus aureus in Malaysia

Abstract

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.

FIG. 1.

Number of MRSA strains isolated from different types of specimens: pus, cellulites, and abscess, referred as wound and soft-tissue infections; respiratory specimens (pulmonary secretion, sputum, and tracheal aspirate); medical devices (central nervous system tip and catheter); cerebrospinal fluid (CSF); conjunctiva; body fluids (peritonea and synovial); and bone marrow.

FIG. 2.

Phylogenic tree of MRSA strains included in the present study showing the combination of data from spa typing, MLST, and SCCmec typing. The tree is a dendrogram based on the unweighted pair group method using average linkages (UPGMA) and constructed based on the pairwise differences in the MLST allelic profiles. The numbers above the row lines demonstrate the genetic distances between the strains: two isolates that differ at one of seven loci differ at a distance of 14.3% (1/7). The diagram shows distances along each branch as 7.1%, half that of the single-locus difference. In this way the distance between ST-239 and ST-1283, defined by a single locus, is 7.1% whereas for ST-1 and ST-188, with two different loci, the distance is again 14.3%.