Staphylococcus aureus ST398 gene expression profiling during ex vivo colonization of porcine nasal epithelium

Background Staphylococcus aureus is a common human and animal opportunistic pathogen. In humans nasal carriage of S. aureus is a risk factor for various infections. Methicillin-resistant S. aureus ST398 is highly prevalent in pigs in Europe and North America. The mechanism of successful pig colonization by MRSA ST398 is poorly understood. Previously, we developed a nasal colonization model of porcine nasal mucosa explants to identify molecular traits involved in nasal MRSA colonization of pigs. Results We report the analysis of changes in the transcription of MRSA ST398 strain S0462 during colonization on the explant epithelium. Major regulated genes were encoding metabolic processes and regulation of these genes may represent metabolic adaptation to nasal mucosa explants. Colonization was not accompanied by significant changes in transcripts of the main virulence associated genes or known human colonization factors. Here, we documented regulation of two genes which have potential influence on S. aureus colonization; cysteine extracellular proteinase (scpA) and von Willebrand factor-binding protein (vWbp, encoded on SaPIbov5). Colonization with isogenic-deletion strains (?vwbp and ?scpA) did not alter the ex vivo nasal S. aureus colonization compared to wild type. Conclusions Our results suggest that nasal colonization with MRSA ST398 is a complex event that is accompanied with changes in bacterial gene expression regulation and metabolic adaptation.BN/BionanoscienceApplied Science

The role of bacterial stimuli in inflammation-driven bone formation

Immune cells and their soluble factors regulate skeletal cells during normal bone regeneration and pathological bone formation. Bacterial infections can trigger immune responses that activate pro-osteogenic pathways, but these are usually overshadowed by osteolysis and concerns of systemic inflammation. The aim of this study was to determine whether the transient local inflammatory reaction to non-viable bacterial immune agonists could lead to favourable new bone formation. In a series of rabbit studies, as proof-of-concept, how tibial intramedullary injection of viable or killed bacterial species affected bone remodelling and new bone formation was determined. Application of killed bacteria led to considerable new bone formation after 4 weeks, without the prolonged systemic inflammation and exaggerated bone lysis seen with active infection. The osteo-immunomodulatory effects of various species of killed bacteria and the dose response relationship were subsequently screened in ectopically-implanted ceramic scaffolds. Histomorphometry after 8 weeks showed that a relatively low dose of killed bacteria enhanced ectopic bone induction. Moreover, lipoteichoic acid - the bacterial cell-wall derived toll-like-receptor (TLR)-2 activator - was identified as an osteo-stimulatory factor. Collectively, the data indicated that bacterial stimuli could be harnessed to stimulate osteogenesis, which occurs through a synergy with osteoinductive signals. This finding holds promise for the use of non-viable bacteria, bacterial antigens, or their simplified analogues as immuno-modulatory bone regenerating tools in bone biomaterials.Biomaterials & Tissue Biomechanic

In Vivo Prevention of Implant-Associated Infections Caused by Antibiotic-Resistant Bacteria through Biofunctionalization of Additively Manufactured Porous Titanium

Additively manufactured (AM) porous titanium implants may have an increased risk of implant-associated infection (IAI) due to their huge internal surfaces. However, the same surface, when biofunctionalized, can be used to prevent IAI. Here, we used a rat implant infection model to evaluate the biocompatibility and infection prevention performance of AM porous titanium against bioluminescent methicillin-resistant Staphylococcus aureus (MRSA). The specimens were biofunctionalized with Ag nanoparticles (NPs) using plasma electrolytic oxidation (PEO). Infection was initiated using either intramedullary injection in vivo or with in vitro inoculation of the implant prior to implantation. Nontreated (NT) implants were compared with PEO-treated implants with Ag NPs (PT-Ag), without Ag NPs (PT) and infection without an implant. After 7 days, the bacterial load and bone morphological changes were evaluated. When infection was initiated through in vivo injection, the presence of the implant did not enhance the infection, indicating that this technique may not assess the prevention but rather the treatment of IAIs. Following in vitro inoculation, the bacterial load on the implant and in the peri-implant bony tissue was reduced by over 90% for the PT-Ag implants compared to the PT and NT implants. All infected groups had enhanced osteomyelitis scores compared to the noninfected controls.Biomaterials & Tissue Biomechanic