Fifty-two (35.6%) tested isolates were classified as biofilm positive. Strains biofilm positive by the MtP method in correlation to the genotype and the medium used are listed in Table 3. Thirty-one out of the ica-positive isolates produced biofilms irrespective of the conditions used – standard or inducing. Among these ica-positive

strains, one was able to produce biofilms only in TSB and five only on TSB-supplemented medium. In contrast, most of the ica-negative isolates (11/15) formed biofilms only in TSB. The difference in the ability of S. epidermidis isolates to form biofilms under optimal conditions was statistically significant (P<0.0001). MtP, CRA and/or PCR methods PF-02341066 purchase have been used by many researchers to determine the crucial virulence factors of CoNS, i.e. the ability of biofilm formation (Christensen et al., 1985; Freeman et al., 1989; Arciola et al., 2002, 2006; Bozkurt et al., 2009; El-Mahallawy et al., 2009). Some reports (Frebourg et al., 2000; Galdbart et al., 2000; Vandecasteele et al., 2003; Chokr et al., 2006; Satorres & Alcaráz, 2007; Mateo et al., 2008; Jain & Agarwal, 2009) indicate that these methods, alone or in combination, can be

useful to discriminate between colonizing or commensal and invasive staphylococcal strains and can lead to the early detection and management of potentially pathogenic isolates responsible for device-associated nosocomial infections. In this study, using three in vitro screening procedures (the MtP method, the CRA test Methane monooxygenase and RG7204 cost the PCR technique), we tested 146 nasopharyngeal S. epidermidis strains. Only 57.5% of all the strains tested exhibited a positive phenotype (biofilm and slime positive) in both MtP and CRA methods. As found by Arciola et al. (2006), 80% of S. epidermidis strains isolated from orthopedic implant infections yielded matching results using both these methods. Moreover, several studies have reported a significant

difference between sensitivity, 7.6% (Mathur et al., 2006) and 75.86% (Jain & Agarwal, 2009), of the CRA test evaluated using the MtP method as a gold standard of biofilm production. In our study, the sensitivity of the CRA test was 73.1% for all the strains tested. Molecular techniques, including traditional PCR or real-time PCR, have been proposed recently for the detection of genes playing a crucial role in the pathogenicity of bacteria (Frebourg et al., 2000; Miyamoto et al., 2003; Arciola et al., 2006; Liberto et al., 2007). In S. epidermidis, the ica operon appears to play an important role in biofilm formation, and consequently, in the pathogenesis of infections associated with indwelling or implanted medical devices (Cafiso et al., 2004; Mack et al., 2004, 2007; Maira-Litran et al., 2004; O’Gara, 2007; Stevens et al., 2008). As found by other authors (Ziebuhr et al., 1997; Frebourg et al., 2000; Miyamoto et al., 2003; Vandecasteele et al., 2003; de Allori et al., 2006; Satorres & Alcaráz, 2007), the majority of S.