Staphylococcus aureus and Staphylococcus epidermidis are the leading etiologic agents of implant-related infections. Biofilm formation is the main pathogenetic mechanism leading to the chronicity and irreducibility of infections. The extracellular polymeric substances of staphylococcal biofilms are the polysaccharide intercellular adhesin (PIA), extracellular-DNA, proteins, and amyloid fibrils. PIA is a poly-β(1-6)-N-acetylglucosamine (PNAG), partially deacetylated, positively charged, whose synthesis is mediated by the icaADBC locus. DNA sequences homologous to ica locus are present in many coagulase-negative staphylococcal species, among which S. lugdunensis, however, produces a biofilm prevalently consisting of proteins. The product of icaA is an N-acetylglucosaminyltransferase that synthetizes PIA oligomers from UDP-N-acetylglucosamine. The product of icaD gives optimal efficiency to IcaA. The product of icaC is involved in the externalization of the nascent polysaccharide. The product of icaB is an N-deacetylase responsible for the partial deacetylation of PIA. The expression of ica locus is affected by environmental conditions. In S. aureus and S. epidermidis ica-independent alternative mechanisms of biofilm production have been described. S. epidermidis and S. aureus undergo to a phase variation for the biofilm production that has been ascribed, in turn, to the transposition of an insertion sequence in the icaC gene or to the expansion/contraction of a tandem repeat naturally harbored within icaC. A role is played by the quorum sensing system, which negatively regulates biofilm formation, favoring the dispersal phase that disseminates bacteria to new infection sites. Interfering with the QS system is a much debated strategy to combat biofilm-related infections. In the search of vaccines against staphylococcal infections deacetylated PNAG retained on the surface of S. aureus favors opsonophagocytosis and is a potential candidate for immune-protection.

Infection is still the major complication of orthopedic implants and projections based on the actual trend indicate that total hip and knee arthroplasties and their consequent infection burden are destined to greatly increase. Staphylococcus aureus and Staphylococcus epidermidis are the leading etiologic agents of orthopedic implant infection. Here we report on epidemiology of implant-related Staphylococcus infections in orthopedics, also referring to our experience, and focus on the crucial role of bacterial adhesins and on their ability to direct the pathogenesis process. Bacteria initiate implant infection by adhering to biomaterials. In the early steps of infection, adhesins mediate the specific interaction between microbial cells and the extracellular matrix proteins filming biomaterial surface. Then adhesin-mediated anchorage allows bacteria to cling to the biomaterial surface and to produce a biofilm that favors their ability to resist antibiotics. With the aim to prevent implant-related infections, anti-infective and infection-resistant biomaterials are being developed. The research for novel therapeutic strategies is incited by the emergence of antibiotic-resistant bacteria. Vaccines against the adhesins or antisense molecules against virulence genes can open a future in combating implant infections.

Extracellular DNA (eDNA) is an important biofilm component that was recently discovered. Its presence has been initially observed in biofilms of Pseudomonas aeruginosa, Streptococcus intermedius, Streptococcus mutans, then Enterococcus faecalis and staphylococci. Autolysis is the common mechanism by which eDNA is released. In P. aeruginosa eDNA is generated by lysis of a bacterial subpopulation, under control of quorum sensing system. In E. faecalis autolysis proceeds in a fratricide mode, resulting from a process similar to necrosis of eukaryotic cells. In Staphylococcus aureus autolysis originates by an altruistic suicide, i.e., a programmed cell death similar to apoptosis of eukaryotic cells. In S. aureus autolysis is mediated by murein hydrolase, while in S. epidermidis by the autolysin protein AtlE. In P. aeruginosa eDNA is located primarily in the stalks of mushroom-shaped multicellular structures. In S. aureus the crucial role of eDNA in stabilizing biofilm is highlighted by the disgregating effect of DNase I. eDNA represents an important mechanism for horizontal gene transfer in bacteria. eDNA and other microbial structural motifs are recognized by the innate immune system via the TLR family of pattern recognition receptors (PRRs).

Propolis was shown to exert antimicrobial, antioxidant, anti-inflammatory, and anticancer activities. Its composition is influenced by seasonal, climatic and phytogeographic conditions. Further variability derives from the extraction methods. Multi Dynamic Extraction Method (MED) has been recently proposed to improve extracts reproducibility. Here, the cytotoxic/anticancer activity of three MED extracts of poplar-type propolis was assayed on human promyelocytic leukaemia HL60, human monocytic leukaemia THP-1, human osteosarcoma MG63, murine fibroblast L929 and human mesenchymal cells (hMSCs). As far as we are aware of, MG63 cells have never been challenged with propolis before, while few studies have so far addressed the effects of propolis on non-tumor cell lines. Consistent results were observed for all propolis preparations. The extracts turned out mildly cytotoxic toward cancer cells, in particular osteosarcoma cells (IC50: 81.9-86.7 µg/ml). Nonetheless, cytotoxicity was observed also in non-tumor L929 cells, with an even lower IC50. hMSCs demonstrated the lowest sensitivity to propolis (IC50: 258.3-287.2 µg/ml). In THP-1 cells, extracts were found to stimulate apoptosis caspase 3/7 activity. The IC50 values observed with osteosarcoma and leukaemia cells do not support a relevant cytotoxicity (as the figures abundantly exceeded 30 µg/ml), despites some selective activity exhibited with HL60 cells. The results confirm the validity of the extraction method, emphasizing the need to assess the selectivity of the interaction with cancer cells when screening for anticancer-drug candidates.

Staphylococcus warneri is a coagulase negative Staphylococcus (CNS) commonly present in the flora of human epithelia and mucosal membranes. Over the last two decades, similarly to other CNS species, S. warneri has been reported as a new emerging pathogen, capable of causing serious infections usually in association with the presence of implant materials, but, at times, even in the absence of a foreign body and in patients considered immunocompetent. At present, there is still a lack of scientific data on the pathogenesis and epidemiology of this species. The present study investigated a collection of 26 clinical isolates derived from orthopedic infections, some associated with implant materials and others not. Automated ribotyping showed the existence of 5 distinct ribogroups. Except for the least numerous ribogroup consisting of a single isolate, all other ribogroups included at least one strain obtained from an infection not associated with implant materials, suggesting that putative virulence factors necessary for infections even in the absence of a foreign body could be transversal to most ribogroup categories. Orthopedic infections were found to involve S. warneri strains with low antibiotic resistance potential, differing in this respect from the strains isolated at neonatal intensive care units, where this species has been described to figure among the principal causative agents and exhibit an alarming profile of antibiotic resistance.