Existence of multiple SCCmec elements in clinical isolates of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) can be classified into hospital-acquired MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA), based on the associated epidemiological risk factors and their SCCmec types. We therefore studied the diversity and distribution of SCCmec elements among MRSA isolates in our region and also evaluated SCCmec typing as a tool for the classification of MRSA.

Two hundred isolates of MRSA obtained from various clinical specimens were included. The clinical and demographic details of the patients and the epidemiological risk factors for MRSA acquisition were documented. Multiplex PCR was optimized for all the major SCCmec types (I to V). Subtyping of SCCmec type IV (IVb, IVc, IVd, IVh) was carried out by simplex PCR.

Based on epidemiological criteria, CA-MRSA constituted 57  % (114/200) of the the test isolates and HA-MRSA made up 43  % (86/200). The predominant SCCmec type found in our study was type III (62%), followed by type V (52.5%) and type I (47.5%), while type II was carried by a single isolate. Of the 200 isolates, 118 carried multiple SCCmec types and 3 were non-typable.

The existence of multiple SCCmec types in individual MRSA isolates resulted in our inability to categorize many of these isolates as either CA-MRSA or HA-MRSA as defined by the SCCmec type criterion.

The major limitation of the study was that the SCC mec element of MRSA isolates exhibiting multiple types was not sequenced and hence this finding could not be confirmed.