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Staphylococcus aureus, which has its ecological niche in the anterior nares, has been shown to cause a variety of infectious diseases mainly for patients in hemodialysis units. We performed this study to evaluate the prevalence of nasal S. aureus carriage among hemodialysis outpatients, to determine the antimicrobial susceptibility of isolates, to characterize the virulence genes, and to identify associated risk factors. Nares swab specimens were obtained from 70 outpatients on hemodialysis between March and June 2010. Samples were plated immediately onto S. aureus specific media and pattern of antibacterial sensitivity was determined using disk diffusion method. Polymerase chain reaction was used to detect nuc, mecA, and genes encoding staphylococcal toxins. Medical record of patients was explored to determine S.aureus carriage risk factors. Nasal screening identified 42.9% S. aureus carriers with only one (3.3%) methicillin-resistant S. aureus isolate. Among the methicillin-susceptible S. aureus isolates, high rate of penicillin resistance (81.8%) has been detected. The identified risk factors were male gender and age ≤ 30 years. Research of virulence factors showed a high genetic diversity among the 30 S. aureus isolates. Twenty-one (70%) of them had at least one virulence gene, of which 3.3% were Panton-Valentine leukocidin (lukS/F-PV) genes. S. aureus carriage must be screened for at regular intervals in hemodialysis patients. Setting up a bacterial surveillance system is one of the strategies to understand the epidemiology of methicillin-resistant S. aureus, to guide local antibiotic policy and prevent spread of antibiotic-resistant S. aureus.

The aim of this study was to determine the prevalence of nasal carriage of Staphylococcus aureus among patients and personnel of private centers at Casablanca, and to determine the resistance pattern of isolates. The carriage of virulence toxin genes by the methicillin resistant strains was also investigated. This study was conducted from November 2008 to February 2009. Nasal swabs were taken from 145 and 42 patients and personnel respectively. The susceptibility testing to 16 antibiotics was performed using the agar disc diffusion method. Minimum inhibitory concentrations (MICs) of oxacillin were determined by the agar dilution method for all strains demonstrating resistance to cefoxitin. In addition, resistant isolates were examined for the existence of the mecA gene by polymerase chain reaction (PCR). Furthermore, the carriage of 22 virulence toxin genes among strains showing resistance to cefoxitin was investigated by PCR Multiplex. The prevalence of nasal carriage of S. aureus was 32.4% (n=47) and 38.1% (n=16) in patients and personnel, respectively. Patients' strains showed 16 resistance patterns against only 4 in personnel strains. No S. aureus isolates were found to be resistant to lincomycin, pristinamycin, gentamicin, chloramphenicol, trimethoprim-sulfamethoxazole, rifampicin and vancomycin, while over 90% (n = 59) were resistant to penicillin G. For the other antibiotics, the percentage of resistance varied between 2.63 and 18.75%. One S. aureus (1.6%) was methicillin resistant by possession of mecA gene. This isolate harboured the staphylococcal enterotoxin genes sec, sed, sell, selm, selo, ser and toxic shock syndrome toxin gene (tst). Investigation of S. aureus nasal carriage and characterization of isolates among patients undergoing hemodialysis is important to develop infection prevention and to limit the spread of methicillin resistant S. aureus (MRSA) strains.