Molecular investigation of staphylococcal cassette chromosome mec types and genotypic relations of methicillin-resistant staphylococci isolated from before and after hospital exposed students.

Background: Reservoir of methicillin resistance genes called staphylococcal cassette chromosome mec (SCCmec), plasmids and genomic characterisations of isolates have been widely investigated in epidemiologic research. However, the extent to which these organisms are transported by patients or hospital staff is not entirely clear.

Aim: This study aims to investigate the molecular relatedness and plasmid profiles of MR staphylococci isolated from nursing students before and after hospital training, to find out the possible source.

Materials and Methods: This study examined 39 methicillin-resistant (MR) staphylococci and 2 inducible clindamycin-resistant, methicillin-susceptible Staphylococcus aureus. Specimens were collected before and after 4 months of hospital training from the hands and nares of 75 nursing students. A polymerase chain reaction technique was used to confirm the existence of mecA gene and identify SCCmec types; total DNA was digested by SmaI endonuclease restriction to monitorise clonal relatedness by pulsed-field gel electrophoresis (PFGE); plasmid profiles were monitorised on agarose gel.

Results: All 39 isolates tested positive for mecA; SCCmec type III was observed most frequently. Interestingly, in one isolate of Staphylococcus epidermidis, four different types of SCCmec elements were observed. There were 23 different types of plasmids, whose sizes ranged from 1.4 to 46.0 kb. After PFGE dendogram analysis, two strains were classified as indistinguishable; six were closely related. Most of the isolates obtained after hospital training showed clonal similarity and seven had multiple SCCmec elements require further investigation for the possible mechanism.

Conclusion: Most of the isolates obtained after hospital training showed clonal similarity and seven had multiple SCCmec elements require further investigation for the possible mechanism.