Comparison between Staphylococcus aureus, strains isolated from medical students in pre-clinical formation and clinical training

OBJECTIVE: To establish the differences between Staphylococcus aureus isolates from medical students in pre-clinical and clinical training and identify the level of susceptibility to methicillin, vancomycin and alternative antibiotics. MATERIALS AND METHODS: A cross-sectional observational design with non-random sampling was used in medical students during pre-clinical and clinical training. Samples were taken from nasal swabs and cultured on blood agar. For beta-hemolytic gram-positive cocci, catalase and coagulase tests were performed and then cultured on mannitol salt agar. Susceptibility to cefoxitin, oxacillin, linezolid, clindamycin and trimethoprim sulfamethoxazole was assessed by using the Kirby-Bauer technique, and for vancomycin, an E-test was performed (Biomerieux®). RESULTS: 51 strains of S. aureus from nasal swabs were isolated from 112 medical students. 68.6% were identifi ed as methicillinsensitive (MSSA) and 31.4% as methicillin-resistant (MRSA). Four MRSA strains showed vancomycin intermediate (VISA 4-8 μg/mL) profile, 41% of MSSA isolates was resistant to clindamycin, 31% to linezolid and 23.5% to trimethoprim sulfamethoxazole. DISCUSSION: MSSA, MRSA and VISA strains are present in nostrils of our medical students, with MRSA showing high resistance levels (>50%) to clindamycin, TMP-SMX and linezolid, and MSSA levels up to 40%. These findings reiterate the need to accomplish good nasal and hands hygiene in order to minimize the spread of S. aureus in community and healthcare facilities