A higher percentage of MSSA (14%) than MRSA (0%) was found positive for slime producing ability, in concordance to the more important Bucladesine in vitro role of PIA/PNAG in MSSA than in MRSA Fulvestrant ic50 biofilm development [8]. Addition of sucrose to CRA did not influence slime formation, suggesting that slime formation was carbohydrates independent. The results were consistent with previous findings in MRSA and MSSA isolates of O’Neill et al. In

MSSA isolates increased ica expression and PIA/PNAG production (as determined with PIA/PNAG immunoblot) was correlated with 4% NaCl-induced biofilm formation, but not with glucose-induced biofilm production [8]. In addition, in MRSA, ica operon transcription was more potently activated by NaCl than by glucose, but did not result in PIA/PNAG formation [8]. Since it has recently been suggested that, in general, PIA/PNAG is a minor matrix component of S. aureus biofilms [5, 9], and thus possibly hardly detectable by CRA screening,

a low prevalence of slime producing strains was expected. Knobloch et al. and check details Mathur et al. reported a positive CRA assay result in only 4-5% of the S. aureus strains tested, in relative accordance with the results of this study, while Grinholc et al. mentioned 47% and 69% for MRSA and MSSA, respectively [16–18]. Jain et al. reported differences between blood stream isolates and commensal S. aureus isolates with regard to positive CRA screening, 75% and 20%, respectively [20]. The variations could be due to differences in genetic backgrounds of the strains used, or to differences in interpretation of the colonies. The definition of slime-forming strains used by Grinholc et al. and Jain et al. was based on the color of the colonies and not on the morphology. Furthermore, they both found a high consistency (96% and 91%, respectively) between CRA screening and biofilm biomass crystal violet staining [17, 20]. In contrast, C-X-C chemokine receptor type 7 (CXCR-7) both in this study, as well in the studies by Knobloch et al., Rode et al., and Mathur

et al. [16, 18, 21], no correlation was found between slime producing MRSA and MSSA isolates and an enhanced tendency to form large amounts of biomass. These studies strongly suggest that CRA screening forms no alternative for crystal violet staining to detect biofilm formation. Probably, the cell to cell adhesion, stimulated by the formation of PIA/PNAG, is less efficient than the expression of surface adhesins, in their contribution to produce more biomass. As described before, the agr genotypes were strictly associated with the clonal lineages [22, 23]. However, exceptions have been observed [24–27] which might be due to interstrain recombination and intrastrain rearrangements [28]. The association between agr genotypes and the genetic background explains the absence of a relationship between the enhanced ability to form biofilm and specific agr genotype(s).