Phenotypic Detection and Rate of Nasal Carriage of Heterotypic Borderline Oxacillin Resistant Staphylococcus aureus In Pre-clinical Medical Students from Malaysia
Santhosh D V. Dept.of Microbiology
Melaka Manipal Medical College(Manipalcampus)International Centre for Health Sciences Manipal - 576 104,Karnataka, India Ph.Off:91-0820 2922634,M Fax:91-820-2571905 M-91-9886901222 Email address: email@example.com
Background: We investigated the rate of nasal colonization of heterogeneous Staphylococcus aureus (Methicillin Resistant S. aureus (MRSA), borderline oxacillin resistant S. aureus (BORSA), as well as hetero-resistant patterns exhibited by S.aureus, in 157 pre-clinical medical students from Melaka Manipal Medical College, Manipal University, in order to determine the carrier profile among the student community from Malaysia before they entered the clinics during the phase I stage II of their medical program in India.
Methods: Oxacillin agar screen technique was employed to screen for MRSA. Broth macrodilution method was used to detect Minimum inhibitory concentration (MIC)values ranging between 0.25-16μg/ml. MHA broth incorporated with oxacillin antibiotic was diluted from 0.25μg/ml, 0.5μg/ml, 1μg/ml, 2μg/ml, 4μg/ml, 8μg/ml to 16μg/ml. The Cefoxitin disc diffusion test was done in order to check if BORSA isolated were mecA negative.
Results: Out of the 37 coagulase positive Staphylococcus aureus samples screened, 27 (72.97%) samples showed an MIC range between 0.25μg/ml-1.0μg/ml. Ten (27.02%) samples had the MIC range between 2μg/ml-8μg/ml; out of which 3 (8.10%) samples had an MIC value of 2μg/ml, and 3 (8.10%) samples showed MIC as 4μg/ml, while 4 (10.81%) showed the MIC to be 8μg/ml in broth dilutions. None (0%) showed MIC for 16μg/ml, and the Cefoxitin disk diffusion tests conducted showed that the 37 isolates of CoPS had zones of inhibition >21mm in diameter.
Conclusions: This study revealed the asymptomatic nasal carriage of BORSA (6.49%) and coagulase positive methicillin susceptible (17.53%) Staphylococcus aureus(MSSA) in healthy student volunteers. Ten (27.02%) samples that had MIC values between 2-8μg/ml showed cefoxitin susceptibility, proving the absence of the mecA gene; they were classified as BORSA; while 27 (72.97%) samples that were cefoxitin susceptible mecA negative strains showed MIC values that ranged between 0.25 μg/ml to 1.0 μg/ml, and were classified as MSSA.