Phenotypic antibiotic tolerance of Staphylococcus aureus in implant-related infections: relationship with in vitro colonization of artificial surfaces

When antibiotics fail: a clinical and microbiological perspective on antibiotic tolerance and persistence of Staphylococcus aureus

Staphylococcus aureus is a major human pathogen causing a vast array of infections with significant mortality. Its versatile physiology enables it to adapt to various environments. Specific physiological changes are thought to underlie the frequent failure of antimicrobial therapy despite susceptibility in standard microbiological assays. Bacteria capable of surviving high antibiotic concentrations despite having a genetically susceptible background are described as 'antibiotic tolerant'. In this review, we put current knowledge on environmental triggers and molecular mechanisms of increased antibiotic survival of S. aureus into its clinical context. We discuss animal and clinical evidence of its significance and outline strategies to overcome infections with antibiotic-tolerant S. aureus.

Immunisation With Immunodominant Linear B Cell Epitopes Vaccine of Manganese Transport Protein C Confers Protection against Staphylococcus aureus Infection

Vaccination strategies for Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA) infections have attracted much research attention. Recent efforts have been made to select manganese transport protein C, or manganese binding surface lipoprotein C (MntC), which is a metal ion associated with pathogen nutrition uptake, as potential candidates for an S. aureus vaccine. Although protective humoral immune responses to MntC are well-characterised, much less is known about detailed MntC-specific B cell epitope mapping and particularly epitope vaccines, which are less-time consuming and more convenient. In this study, we generated a recombinant protein rMntC which induced strong antibody response when used for immunisation with CFA/IFA adjuvant. On the basis of the results, linear B cell epitopes within MntC were finely mapped using a series of overlapping synthetic peptides. Further studies indicate that MntC113-136, MntC209-232, and MntC263-286 might be the original linear B-cell immune dominant epitope of MntC, furthermore, three-dimensional (3-d) crystal structure results indicate that the three immunodominant epitopes were displayed on the surface of the MntC antigen. On the basis of immunodominant MntC113-136, MntC209-232, and MntC263-286 peptides, the epitope vaccine for S. aureus induces a high antibody level which is biased to TH2 and provides effective immune protection and strong opsonophagocytic killing activity in vitro against MRSA infection. In summary, the study provides strong proof of the optimisation of MRSA B cell epitope vaccine designs and their use, which was based on the MntC antigen in the development of an MRSA vaccine.

Biofilm-related infections: bridging the gap between clinical management and fundamental aspects of recalcitrance toward antibiotics

Surface-associated microbial communities, called biofilms, are present in all environments. Although biofilms play an important positive role in a variety of ecosystems, they also have many negative effects, including biofilm-related infections in medical settings. The ability of pathogenic biofilms to survive in the presence of high concentrations of antibiotics is called "recalcitrance" and is a characteristic property of the biofilm lifestyle, leading to treatment failure and infection recurrence. This review presents our current understanding of the molecular mechanisms of biofilm recalcitrance toward antibiotics and describes how recent progress has improved our capacity to design original and efficient strategies to prevent or eradicate biofilm-related infections.

Comparison of tigecycline and vancomycin for treatment of experimental foreign-body infection due to methicillin-resistant Staphylococcus aureus

Twice-daily 7-day regimens of tigecycline (7 mg/kg) and vancomycin (50 mg/kg) were compared in a rat tissue cage model of chronic foreign-body infection due to methicillin (meticillin)-resistant Staphylococcus aureus strain MRGR3. Subcutaneously administered tigecycline reached levels in tissue cage fluid that were nearly equivalent or slightly superior to the antibiotic MIC (0.5 microg/ml) for strain MRGR3. After 7 days, equivalent, significant reductions in bacterial counts were recorded for tigecycline-treated and vancomycin-treated rats, compared with those for untreated animals.

Tolerance of staphylococci to bactericidal antibiotics

Antibiotic therapy for deep-seated staphylococcal infections, especially when they are associated with artificial devices used for orthopedic surgery is often associated with failure. Standard anti-staphylococcal bactericidal antibiotics, such as semi-synthetic penicillins, cephalosporins, or glycopeptides, are effective when given prophylactically in clinical conditions or experimental trials of implant-related infections. However, the efficacy of all anti-staphylococcal agents is seriously diminished on already established implant-related deep-seated infections, which then frequently require surgical implant removal to obtain a cure. The failure of antibiotic therapy to cure established staphylococcal foreign-body infections may arise in part from a broad-spectrum phenotypic tolerance expressed in vivo to different classes of antimicrobial agents. The molecular and physiological mechanisms of this in vivo tolerance remain poorly understood.

Intensive therapy with ceftobiprole medocaril of experimental foreign-body infection by methicillin-resistant Staphylococcus aureus

The therapeutic activity of ceftobiprole medocaril, the water-soluble prodrug of ceftobiprole, was compared to that of vancomycin in a rat tissue cage model of chronic methicillin-resistant Staphylococcus aureus (MRSA) foreign-body infection. The MICs and MBCs of ceftobiprole and vancomycin in Mueller-Hinton broth for strain MRGR3 were 1 and 4 and 1 and 2 microg/ml, respectively. In vitro elimination rates of strain MRGR3 of 4 and 8 microg/ml of ceftobiprole or vancomycin were equivalent. After 2 weeks of infection, mean +/- standard error of the mean viable counts of strain MRGR3 were 6.83 +/- 0.11 log CFU/ml of tissue cage fluid (n = 87). High-dose regimens of ceftobiprole medocaril (equivalent to 150 mg/kg of ceftobiprole) or 50 mg/kg vancomycin produced nearly identical average peak and trough levels of ceftobiprole and vancomycin in tissue cage fluid, which exceeded the MBC of either antibiotic towards strain MRGR3 for > or =75% of each dosing interval. After 7 days of therapy with ceftobiprole medocaril or vancomycin, average counts of MRGR3 decreased significantly (P < 0.02) by 0.68 +/- 0.28 (n = 29) and 0.88 +/- 0.22 (n = 28) log CFU/ml of tissue cage fluid, respectively, compared with cages of untreated animals, but were not significantly different from each other. No resistant mutants were detected on ceftobiprole-supplemented agar following therapy with this cephalosporin. The in vivo activity of ceftobiprole medocaril against chronic MRSA foreign-body infections was equivalent to that of vancomycin and did not lead to the emergence of resistant subpopulations.

Implantatinfektionen

Implant-associated infections are a major challenge for the primary care physician because the chance of cure depends on the time interval between infection and start of adequate surgical and antimicrobial treatment. On the other hand, rapid therapy should not prevent from correct microbiological sampling. Since long-term antibiotic therapy is required, the microorganism and its susceptibility pattern should be known. Thus, the primary care physician should know signs and symptoms of these rare infections and rapidly involve the specialist. The main task of the specialist is to confirm the diagnosis and to decide whether the implant has to be removed, or whether debridement with retention is a feasible option to eradicate infection. In this review, infections associated to vascular grafts, to pacemakers and to arthroplasties are presented.