Characterization of resistance to selected antibiotics and Panton-Valentine leukocidin-positive Staphylococcus aureus in a healthy student population at a Malaysian University

Introduction: This study aims to assess the antimicrobial susceptibility profiles of Staphylococcus aureus strains isolated from university students and to determine the prevalence of constitutive and inducible clindamycin resistance, the latter being able to cause therapeutic failure due to false in vitro clindamycin susceptibility.

Methods: S. aureus strains were isolated from the nasal swabs of 200 health sciences students of a Malaysian university. Twelve classes of antibiotics were used to evaluate the antimicrobial susceptibility profiles with the macrolide-lincosamide-streptogramin B (MLS_B) phenotype for inducible clindamycin resistance determined by the double-diffusion test (D-test). Carriage of resistance and virulence genes was performed by PCR on S. aureus isolates that were methicillin resistant, erythromycin resistant and/or positive for the leukocidin gene, pvl (n=15).

Results: Forty-nine isolates were viable and identified as S. aureus with four of the isolates characterized as methicillin-resistant S. aureus (MRSA; 2.0%). All isolates were susceptible to the antibiotics tested except for penicillin (resistance rate of 49%), erythromycin (16%), oxacillin (8%), cefoxitin (8%) and clindamycin (4%). Of the eight erythromycin-resistant isolates, iMLS_B was identified in five isolates (three of which were also MRSA). The majority of the erythromycin-resistant isolates harbored the msrA gene (four iMLS_B) with the remaining iMLS_B isolate harboring the ermC gene.

Conclusion: The presence of MRSA isolates which are also iMLS_B in healthy individuals suggests that nasal carriage may play a role as a potential reservoir for the transmission of these pathogens.