Panton-Valentine leukocidin gene detected in Staphylococcus aureus strain isolated from a knee arthroprosthesis infection.

This report focuses on the molecular characterization of a Staphylococcus aureus strain isolated from a knee arthroprosthesis infection and recognized retrospectively as a carrier of the Panton-Valentine leukocidin gene. The stored microbiological isolate, which belonged to the strain collection of the Research Unit on Implant Infections of the Rizzoli Orthopaedic Institute, was retrieved for molecular analysis. Genotyping was carried out, revealing an interesting profile. In addition to the positivity for the Panton-Valentine toxin gene, the results indicated that the isolate belonged to the agr III group and was endowed with bbp and cna genes, both encoding for staphylococcal adhesins that bind bone proteins. The strain had the mecA gene for methicillin resistance, even though it was unable to resist any of the beta-lactam or other antibiotics. Its gene configuration matched that of other community-acquired methicillin-resistant and methicillin-susceptible Staphylococcus aureus(CA-MRSA and CA-MSSA) strains which have recently been reported worldwide. As far as we know,this is the first report on a PVL-positive S. aureus strain associated with an orthopedic implant (knee arthroprosthesis) infection.

Low-density lipoprotein (LDL) receptor/transferrin fusion protein: in vivo production and functional evaluation as a potential therapeutic tool for lowering plasma LDL cholesterol.

A soluble form of human low-density lipoprotein receptor (LDL-R) fused in frame with rabbit transferrin (LDL-Rs(hu)/Tf(rab)) is assessed in vivo as a therapeutic tool for lowering plasma LDL cholesterol. The cDNA encoding LDL-Rs(hu)/Tf(rab) is expressed in mice, using a hydrodynamics-based gene transfer procedure. The transgene is transcribed in the liver of transduced animals and the corresponding protein is secreted into the bloodstream. Circulating LDL-Rs(hu)/Tf(rab) binds LDL specifically, thus indicating that it is correctly processed through the cellular compartments in vivo. More importantly, the expression of LDL-Rs(hu)/Tf(rab) allows the removal of injected human (125)I-labeled LDL ((123)I-LDL) from the bloodstream of transduced CD1 mice, which show faster LDL plasma clearance, anticipating by approximately 90 min the same clearance value observed in control animals. A similar effect is observed in transduced LDL-R(-/-) mice, in which the clearance of injected human LDL depends solely on the presence of circulating LDL-Rs(hu) /Tf(rab). In these animals the extent of plasma LDL clearance is directly related to the concentration of LDL-Rs(hu)/Tf(rab) in the blood. Finally, LDL-Rs(hu)/Tf(rab) does not alter the pattern of LDL organ distribution: in transduced animals, as well as in control animals, liver and bladder are the predominantly labeled organs after (123)I-LDL injection. However, LDL-Rs(hu)/Tf(rab) has a quantitative effect on LDL tissue deposition: in treated animals LDL-Rs(hu)/Tf(rab) determines an increase in radioactivity in the liver at early times after (123)I-LDL injection and a progressive labeling of the bladder, starting 20 min after injection.

Biofilm extracellular-DNA in 55 Staphylococcus epidermidis clinical isolates from implant infections.

Biofilm formation is broadly recognized as an important virulence factor in many bacterial species implicated in implant-related opportunistic infections. In spite of a long history of research and many investigative efforts aimed at elucidating their chemical composition, structure, and function, the nature of bacterial biofilms still remains only partly revealed. Over the years, different extracellular polymeric substances (EPS) have been described that contribute functionally and structurally to the organization of biofilms. Recently extracellular DNA (eDNA) has emerged as a quantitatively conspicuous and potentially relevant structural component of microbial biofilms of many microbial species, Staphylococcus aureus and S. epidermidis among them. The present study aims at comparatively investigating the amount of eDNA present in the biofilm of 55 clinical isolates of S. epidermidis from postsurgical and biomaterial-related orthopedic infections. Quantification of eDNA was performed by a non-destructive method directly on bacterial biofilms formed under static conditions on the plastic surface of 96-well plates.

Characterization of 26 Staphylococcus warneri isolates from orthopedic infections.

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.