Herren, Sebastian C

Background: Infection following extensor mechanism reconstruction (EMR) with Marlex mesh (C.R. Bard) is devastating and limb-threatening. The purpose of this study was to evaluate whether vancomycin-loaded mesh reduces staphylococcal infection in a murine EMR model. Methods: Mouse-sized, 8-layer mesh constructs were fabricated to simulate clinical reconstruction and soaked in a vancomycin solution (50 mg/mL) for in vitro and in vivo testing. Three methicillin-resistant clinical isolates from human periprosthetic Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus lugdunensis knee infections were evaluated. In vitro testing assessed vancomycin loading capacity, mechanical properties, antibacterial activity, and inhibition of biofilm formation. For in vivo experiments, plain or vancomycin-loaded mesh was implanted into C57BL/6 mouse extensor mechanisms, which were intraoperatively contaminated with 1 of the 3 study isolates (5 per group). Mesh and surrounding tissue were harvested for quantitative culture on postoperative day 9. Results: For all 3 isolates, vancomycin-loaded mesh produced zones of inhibition and exhibited antibacterial activity through at least 3 days in vitro (p < 0.0001). Mechanical testing revealed that loading mesh with vancomycin did not negatively impact tensile strength, hysteresis, or suture pull-through properties. In vitro testing of inhibition of biofilm formation demonstrated reduced colony-forming units 6 hours after inoculation, which remained low throughout the 9-day experimental period (p < 0.05 for all isolates). In vivo, vancomycin-loaded mesh reduced bacterial burden on mesh and in surrounding tissue by >3 log 10 compared with plain mesh for all 3 isolates (p < 0.01 for both mesh and tissue). Conclusions: Vancomycin-loaded mesh provided in vitro antibacterial activity without compromising mesh mechanical properties and reduced staphylococcal infection in a murine EMR model. Further work is needed to evaluate translational potential and safety before clinical application. Clinical Relevance: Mesh-associated infection after EMR is devastating and difficult to treat. These preclinical findings suggest that local vancomycin delivery may serve as an adjunct to systemic prophylaxis, warranting further study before clinical use.

ABSTRACT Lytic phages are a promising consideration to combat recalcitrant bacterial infections. To advance the possibility of using phage therapy in the clinical routine, standardized phage susceptibility testing methods are needed. Here, staphylococcal phage K was tested against 154 periprosthetic joint infection-associated Staphylococcus aureus isolates using a double overlay spot assay in technical and biological triplicates. Individual plaques were assessed using a morphology scoring system ranging from 0 (no plaques) to 4 (large, clear plaques), with scores ≥2 considered indicative of infectivity. Overall, 107 isolates exhibited scores ≥2. The intra-day and inter-day coefficients of variation were 0.9 and 2.5, respectively. Plaque-forming unit per milliliter (PFU/mL) titers correlated with morphology scores (Spearman’s ρ = 0.8, P < 0.0001). The results suggest high precision of the described spot assay assessing S. aureus susceptibility to phage K. IMPORTANCE Standardized laboratory assays for assessing phage susceptibility are a prerequisite for clinical implementation of phage therapy. No assay has been denoted a reference standard. Criteria that can be used to assess assay precision and suitability for routine testing are intermediate precision and repeatability. Here, staphylococcal phage K was tested using the double overlay spot assay against 154 periprosthetic joint infection-associated Staphylococcus aureus isolates in technical and biological triplicates. In addition to measuring phage titers, plaque-forming units were assessed with a scoring system. Results indicate high intermediate precision and repeatability of the method described.

Background: Phages are being assessed for treatment of periprosthetic joint infection (PJI). Staphylococci are the most common cause of PJI. Phages are traditionally considered to be strain-specific and restricted to specific species. We aimed to assess the in vitro activity of a collection of staphylococcal phages against a selection of clinical Staphylococcus isolates recovered from PJI over a 20-year period. Methods: The activity of 37 staphylococcal phages was evaluated against 204 staphylococcal isolates, including 102 Staphylococcus aureus, 81 Staphylococcus epidermidis , and 21 Staphylococcus lugdunensis , using a tetrazolium dye–based metabolic assay. Standardized inocula of bacteria and phage were incubated over 48 hours. Growth inhibition ≥8 hours was considered indicative of phage activity. Results: A total of 7,548 phage-isolate pairs were assessed. Overall, 31 of 37 phages had activity against at least 1 isolate. The most broadly active phage showed activity against 50 of 195 isolates (26%) tested. Twenty-three phages showed cross-species activity, with 11 phages active against all 3 Staphylococcus species, and 12 phages active against 2 species. Of all S. aureus isolates tested, 61% were susceptible to at least 1 phage, while 31% and 76% of S. epidermidis and S. lugdunensis isolates were susceptible to at least 1 phage, respectively. Conclusions: This is the largest library of phages evaluated against staphylococci from PJI. Results show that staphylococcal phages can have cross-species activity, suggesting that phage libraries may offer cross-species coverage of clinically encountered staphylococcal isolates from PJI. Level of Evidence: Level V . Mechanism-based reasoning. See Instructions for Authors for a complete description of levels of evidence.

ABSTRACT Periprosthetic joint infection (PJI) is a serious complication of total joint arthroplasty (TJA), with Staphylococcus aureus being one of the most common causative organisms. Irrigation and debridement with component retention (IDCR) is often performed to manage PJI. Antimicrobial treatment that targets S. aureus biofilms on prosthesis surfaces and within bone may be especially helpful when retaining a prosthesis. Phages, viruses that specifically infect bacteria, are a potential therapeutic consideration. Using a biofilm time kill assay in bovine synovial fluid, bactericidal activity of vancomycin or phage K (32 µg/mL and 10 11 pfu/mL, respectively) as well as the combination of phage K (10 10 pfu/mL) and vancomycin (32 µg/mL) was observed against a methicillin‐resistant S. aureus (MRSA) strain. Using a murine PJI model, mice infected with MRSA underwent IDCR followed by phage administration into the joint space with or without systemically administered vancomycin. Mice receiving both phage and vancomycin had significant reductions in MRSA on the prosthesis surface compared to untreated or vancomycin‐treated mice. Phage K showed bactericidal activity in vitro and was active when locally delivered in combination with systemically administered vancomycin in a murine PJI model managed with IDCR.

ABSTRACT Contezolid has activity against methicillin-resistant Staphylococcus aureus (MRSA), a common cause of orthopedic infection. In a rat model of foreign body osteomyelitis, 1.3 log 10 cfu/g bone and 0.5 log 10 cfu/k-wire reduction in MRSA was found in tibiae ( P = 0.0186) and K-wires, respectively, of contezolid-treated compared to untreated rats. No MRSA was recovered from animals receiving rifampin alone or in combination with contezolid or vancomycin. There was no emergence of resistance to contezolid, vancomycin, or rifampin.

A novel Corynebacterium species, strain BD556T, isolated from blood, was identified at Mayo Clinic, Rochester, MN, USA. After failing definitive identification using MALDI-ToF MS and partial 16S rRNA gene sequencing, BD556T was characterized using a polyphasic approach, including phenotypic, biochemical and whole-genome sequencing methods. BD556T was a Gram-positive rod with clubbed ends, facultatively anaerobic, catalase-positive, oxidase-negative and non-motile. Colonies were white, opaque and non-haemolytic with halo-like edges. BD556T grew at 35 °C in room air, with CO2 and under anaerobic conditions. BD556T grew well in 0 and 6% NaCl and weakly in 10% NaCl. The genome size was 2 349 779 bp with a G+C content of 60.39%. Phylogenetic analysis using 16S rRNA gene sequence analysis, average nucleotide identity and digital DNA–DNA hybridization between the genome of BD556T and the closest type strains from the Type Strain Genome Server database yielded separation values well beyond those required for species delineation. Chemotaxonomic analyses of BD556T revealed ribose, arabinose and galactose as whole-cell sugars and an A1γ meso-diaminopimelic acid-direct peptidoglycan type. The major cellular fatty acids were C15 : 0 (21.0%), C16 : 0 (14.8%), C17 : 1 ω9c (26.2%), C17 : 0 (13.3%) and C18 : 1 ω9c (18.3%). Polar lipids included diphosphatidylglycerol, phosphatidylglycerol and unidentified glycolipids and phospholipids. BD556T also contained mycolic acids (32–36 carbons) typical of corynebacteria. The respiratory quinones were dominated by MK-8(H2) (71.2%) and MK-9(H2) (25.9%), with smaller amounts of MK-7(H2) and MK-10(H2). The results presented support the tenet that BD556T (=TSD 427T=NCTC 15078T) is a novel species for which the name Corynebacterium mayonis sp. nov. is proposed.

ABSTRACT Phage therapy has not been established in the clinical routine, in part due to uncertainties concerning efficacy and immunogenicity. Here, three rabbits were immunized against staphylococcal phage K to assess viral potency in the presence of immunized serum. Three rabbits received weekly intramuscular injections of ~10 10±1 pfu/mL phage K. Phage K-specific IgG formation was measured by an enzyme-linked immunosorbent assay (ELISA); phage inactivation was assessed by calculating K-rates. Using transmission electron microscopy (TEM) and immunogold labeling, antibody binding to phage K was visualized. This was numerically assessed by objective imaging analysis comparing the relative distances of each gold particle to the nearest phage head and tail structure. Immunization led to a strong IgG response, plateauing 7 days after the last phage injection. There was no significant correlation between K-rate and antibody titer over time. TEM showed IgG binding to the head structure of phage K. Image analysis showed a significant reduction in relative distances between antibodies and phage head structures when comparing samples from day 0 and day 28 ( P < 0.0001). These results suggest that while individual serum analysis for antibodies against therapeutic phage bears consideration prior to and with prolonged therapy, during phage application, the formation of specific antibodies against phage may only partially explain decreased phage potency in the presence of immunized serum. Instead, other factors may contribute to an individual’s “humoral receptiveness” to phage therapy. Future investigations should be directed toward the identification of the humoral factors that have the most significant predictive value on phage potency in vivo .