Staphylococcal cassette chromosome (SCCmec) typing of methicillin-resistant Staphylococcus aureus strains isolated from healthy workers nasal swabs in Larestan hospitals

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important causes of opportunistic infections in the community as well as hospitals. Nowadays, an increase in the antibiotic resistance has caused concern to the medical community. Meanwhile, resistance to methicillin is important because of limiting treatment. This study was conducted to track methicillin resistance gene and to type staphylococcal cassette chromosome (SCCmec) in S. aureus strains isolated from nasal swabs of healthy hospital workers and to determine the antibiotic sensitivity pattern of the strains.
In this descriptive cross-sectional study, 230 specimens were collected from healthy workers nasal swabs of Larestan hospital during 2015. S. aureus strains were identified using laboratory standard methods. The antibiotic susceptibility pattern was characterized using disk diffusion test, minimum inhibitory concentration (MIC) was determined by E-test and sensitivity to methicillin was assessed by agar screening test. Furthermore, the presence of antibiotic-resistant mecA gene and SCCmec genotyping were investigated using the multiplex-PCR method.
Among all nasal swab samples, 37 (14.8%) S. aureus isolates were recovered. 28 (75.7%) out of 37 S. aureus isolates were confirmed as MRSA. 21 (75%) of 28 MRSA isolates were community-associated MRSA (CA-MRSA), and the remaining 7 (25%) were hospital-acquired MRSA (HA-MRSA). SCCmec genotyping showed the most frequent isolates as follows: 9 (32.1%) isolates as SCCmec type I, 8 (28.6%) isolates as SCCmec type IV, 5 (17.9%) isolates as SCCmec type II, 4 (14.3%) isolates as SCCmec type V and 2 (7.1%) isolates as SCCmec type III. Evaluation of antibiotic resistance pattern showed the highest resistance to penicillin (100%) and oxacillin (60%) respectively, and the lowest resistance to vancomycin (0%). E-test results confirmed 28.5% of the isolates as intermediate vancomycin-resistant. Using agar screening test, oxacillin resistance was shown as 92.8%.
Our result showed that 70% methicillin resistance in the S. aureus which is mostly CA-MRSA strains. This could be a serious warning about the need to treat infections caused by this bacterium and control the carriers in the hospital environment