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Staphylococcus lugdunensis is an unusually virulent coagulase-negative species, which causes serious infection similar to S. aureus. We evaluated the expression of virulence factors such as S. lugdunensis synergistic haemolysin (SLUSH), fibrinogen-binding protein (Fbl), biofilm production and biofilm-production-related genes in 23 S. lugdunensis clinical isolates and one type strain that had been previously characterized for their genotypes. In addition, the biofilm composition and the ability of isolates to adhere to and invade human epithelial lung cells were also investigated. The PCR method used detected the presence of slush and intercellular adhesin (ica) virulence genes in all isolates. All isolates produced the Fbl protein and, with the exception of the type strain, all isolates produced the SLUSH haemolysin. Fourteen (60.9 %) isolates produced biofilms. The detachment assay, using sodium metaperiodate or proteolytic enzymes to analyse the biofilm composition, showed protein-mediated biofilms in two representative isolates, one for each colony type (rough and smooth). All strongly biofilm-producing isolates, including three with rough colony morphology, had the same prevalent PFGE pattern. However, among the representative strains tested, only the S. lugdunensis isolate that formed rough colonies was able to adhere to and invade A549 cell monolayers in the same quantities as those observed with S. aureus isolates (P = 1.000). No significant adhesion or invasion was observed for the other isolates in comparison with the S. aureus isolate, independent of biofilm production or clonality. Our results could explain the incredible ability of this pathogen to cause infections that are as aggressive as S. aureus. In addition, the ability of S. lugdunensis to adhere to and invade eukaryotic cells was also noticed for isolates with rough colony morphology, reinforcing the increased virulence in this species.

Background: We evaluated the relationship among hospital infection and colonization by methicillin-susceptible Staphylococcus aureus (MSSA), clonal spread, and associated risk factors in a neonatal intensive care unit (NICU) of the Uberlândia Federal University-affiliated hospital in Brazil., Methods: Between February 2004 and June 2005, a longitudinal surveillance study was carried out in an NICU with neonates presenting infections, through both the NNIS system and S aureus punctual colonization prevalence inquests., Results: The overall rate of infection incidence was 23/1000 patient-days. Of all the neonates assessed, 15 were infected and 15 colonized. Sepsis was the most frequent infection, whereas anterior nare was the most isolated site. Antibiotics use, central vascular catheter (CVC), and CVC use more than 7 days and its insertion by phlebotomy were the risk factors for colonization/infection. Molecular analysis showed polyclonal origin (12 genotypes), with predominance of a genotype ("B"), and clonal identity between colonization and infection samples., Conclusion: The analysis by means of classical epidemiology and molecular techniques pointed out that methicillin-susceptible Staphylococcus aureus infections were associated with previous colonization by the pathogen, with evidence of horizontal transmission within the unit.