Prevalence and Antibiotic Resistance Profiles of Staphylococcus aureus Isolated from the Nasal Mucosa of Medical Students at University Center in the Northwest Region, Rio de Janeiro, Brazil

Abstract

Background and Aim: Nasal colonization by Staphylococcus aureus, particularly among healthcare workers and students exposed to hospital environments, constitutes a significant risk factor for infection and dissemination of multidrug-resistant strains such as MRSA (methicillin-resistant Staphylococcus aureus) and VRSA (vancomycin-resistant Staphylococcus aureus). This research aimed to determine the prevalence of nasal colonization by Staphylococcus aureus and to characterize the antimicrobial resistance profiles of isolates obtained from medical students at a university center in the northwest region of the province of Rio de Janeiro, Brazil. Methods: A cross-sectional, descriptive, and observational study was conducted involving 100 medical students in the early stages of hospital exposure. Nasal swabs were collected from both anterior nares, cultured on mannitol salt agar and sheep blood agar, and incubated at 37°C. Identification of Staphylococcus aureus was based on morphological and biochemical tests. Antibiotic susceptibility was assessed by the Kirby-Bauer disk diffusion method, testing 15 antibiotics. Results: The prevalence of nasal colonization by Staphylococcus aureus was 25%. High rates of resistance to beta-lactam antibiotics were observed (92%), with lower sensitivity to cefoxitin (20%) and oxacillin (32%). Vancomycin resistance was detected in 20% of strains, with 4% exhibiting susceptibility with increased exposure in disk diffusion, but definitive resistance results demand more tests to determine the Minimum Inhibitory Concentration. All isolates were susceptible to linezolid. Concomitant resistance to beta-lactams and evidences of vancomycin resistance indicates the emergence of multidrug resistance, despite susceptibility to other antibiotic such as ciprofloxacin and rifampicin. Conclusion: High resistance rates of some strains highlight possible clinical challenges in infection management. Continuous surveillance, molecular characterization of resistance mechanisms, antimicrobial stewardship programs, and preventive measures, including targeted decolonization strategies, are essential to control the dissemination of clinically high-risk Staphylococcus aureus strains in healthcare settings and to protect patients and other susceptible individuals.