[Genotyping of nosocomial methicillin-resistant Staphylococcus aureus strains isolated from clinical specimens by...

Methicillin-resistant Staphylococcus aureus (MRSA) infections are associated with increased cost, mortality and length of hospital stay compared with the other infections. Therefore, controlling the spread of this pathogen by screening patients, personnel and the environment remains as a high priority in infection control programs. The aim of this study was to detect the clonal relationship between nosocomial MRSA strains by using repetitive-sequence-based polymerase chain reaction (rep-PCR) method which has several advantages owing to its speed and ease of use. A total of 100 MRSA stock strains that had been isolated from various clinical samples of hospitalized patients in Erciyes University Medical Faculty Hospitals between September 2008-October 2009, were included in the study. Methicillin resistance of the strains were determined by cefoxitin disc diffusion test according to CLSI guidelines. Rep-PCR (Diversilab, bioMerieux, France) method was performed in the following four steps in order to determine genetic proximity of MRSA strains: (1) Manual DNA extraction (UltraClean Microbial DNA Isolation Kit; MoBio Laboratories, USA), (2) Rep-PCR by using fingerprinting kits in the thermocycler (Diversilab DNA Fingerprinting Kit), (3) Automated microfluidic electrophoresis by bioanalyzer (Diversilab DNA LabChip kit), (4) Analysis and rapid evaluation with the use of web-based DiversiLab software (version 2.1.66). Rep-PCR analysis have shown the presence of a total 11 clones, including 3 major clones [A (4 subtypes), B (2 subtypes) and C (2 subtypes)] and 8 unique clones (DK). Clone A was found to be the dominant type. Seventy-eight percent of the 100 MRSA isolates belonged to clone A (63 were A1; 9 were A2; 4 were A3, 2 were A4), 11% belonged to clone B (10 were B1, 1 was B2), 3% belonged to clone C (2 were C1, 1 was C2), and one of each belonged to the other clones (D, E, F, G, H, I, J, K). Clone A was isolated from 93.3% (14/15) of the samples sent from internal diseases intensive care unit (ICU), from 66.6% (10/15) of the samples sent from infectious diseases ward and 91% (10/11) of hematology-oncology ward samples. All MRSA strains isolated from anesthesiology and newborn ICU were of clone A. The isolation dates of these strains were in proximity. In conclusion, MRSA strains showed clonal dissemination in our hospital, clone A being the predominant one during the study period. Rep-PCR which is a rapid and reliable method, can easily be applied for molecular epidemiological purposes and aid to infection control measures.