Prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infection and the molecular characteristics of MRSA bacteraemia over a two-year period in a tertiary teaching hospital in Malaysia

Abstract

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is an established pathogen that causes hospital- and community-acquired infections worldwide. The prevalence rate of MRSA infections were reported to be the highest in Asia. As there is limited epidemiological study being done in Malaysia, this study aimed to determine the prevalence of MRSA infection and the molecular characteristics of MRSA bacteraemia.

Methods: Two hundred and nine MRSA strains from year 2011 to 2012 were collected from a tertiary teaching hospital in Malaysia. The strains were characterized by antimicrobial susceptibility testing, staphylococcal cassette chromosome mec (SCCmec) typing, detection of Panton-Valentine leukocidin (PVL) gene, multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Patient's demographic and clinical data were collected and correlated with molecular data by statistical analysis.

Results: Male gender and patient >50 years of age (p < 0.0001) were significantly associated with the increased risk of MRSA acquisition. Fifty-nine percent of MRSA strains were HA-MRSA that carried SCCmec type II, III, IV and V while 31% were CA-MRSA strains with SCCmec III, IV and V. The prevalence of PVL gene among 2011 MRSA strains was 5.3% and no PVL gene was detected in 2012 MRSA strains. All of the strains were sensitive to vancomycin. However, vancomycin MIC creep phenomenon was demonstrated by the increased number of MRSA strains with MIC ≥1.5 μg/mL (p = 0.008) between 2011 and 2012. Skin disease (p = 0.034) and SCCmec type III (p = 0.0001) were found to be significantly associated with high vancomycin MIC. Forty-four percent of MRSA strains from blood, were further subtyped by MLST and PFGE. Most of the bacteraemia cases were primary bacteraemia and the common comorbidities were diabetes, hypertension and chronic kidney disease. The predominant pulsotype was pulsotype C exhibited by SCCmec III-ST239. This is a first study in Malaysia that reported the occurrence of MRSA clones such as SCCmec V-ST5, untypeable-ST508, SCCmec IV-ST1 and SCCmec IV-ST1137.

Conclusions: SCCmec type III remained predominant among the MRSA strains in this hospital. The occurrence of SCCmec IV and V among hospital strains and the presence of SCCmec III in CA-MRSA strains are increasing. MRSA strains causing bacteraemia over the two-year study period were found to be genetically diverse.

Keywords: MLST; MRSA Bacteraemia; Methicillin-resistant Staphylococcus aureus (MRSA); PFGE; SCCmec types.

Fig. 1

Dendrogram of MRSA PFGE patterns generated by UPGMA clustering method using Dice coefficient. The dotted line indicates an arbitrary 80% similarity demarcation

Fig. 2

Population snapshot of MRSA strains from blood source in the MLST database. Individual sequence type (ST) is highlighted in black (STs in the database), green (STs in this study) and pink (STs in both the database and in this study) and is represented by each circle. The size of the circle indicates the frequency of a particular ST and the colour of the circle represents founders or subgroup founders. Blue circles are ‘founders’ [defined as ST with many single locus variants (SLVs) and is prevalent within a CC], whereas yellow circle are ‘subgroup founders’. The most prevalent ST in this study was ST239, which is the subgroup founder within CC8