d HY-133 is a recombinant bacteriophage endolysin with bactericidal activity against Staphylococcus aureus. Here, HY-133 showed in vitro activity against major African methicillin-susceptible and methicillin-resistant S. aureus lineages and ceftaroline/ceftobiprole-and borderline oxacillin-resistant isolates. HY-133 was also active against Staphylococcus schweitzeri, a recently described species of the S. aureus complex. The activity of HY-133 on the tested isolates (MIC 50 , 0.25 g/ml; MIC 90 , 0.5 g/ml; range, 0.125 to 0.5 g/ml) was independent of the species and strain background or antibiotic resistance. Bacteriophage endolysins are peptidoglycan hydrolases with strong species-specific bactericidal activity (1). Endolysins are considered a potential new class of antimicrobial agents which could be used both for decolonization of methicillin-resistant Staphylococcus aureus (MRSA) and invasive infections, as animal models have revealed (1). Indeed, there is a need for the development of new antimicrobial agents, in particular against S. aureus infections, as resistance rates are rising not only in industrialized countries but also in so-called developing regions, such as subSaharan Africa (2).Similar to its progenitor PRF-119 (3), HY-133 (owned by Hyglos GmbH, Bernried, Germany) is an optimized, recombinantly produced chimeric bacteriophage endolysin which has a pronounced bactericidal activity against S. aureus and an increased proteolytic stability due to a shortened linker peptide (4). These chimeric endolysins consist of an enzymatic active domain (EAD), a cysteine-and histidine-dependent aminopeptidase/hydrolase (CHAP) from the endolysin of phage K, and a cell wallbinding domain (CBD) from lysostaphin (3, 4).While the progenitor molecule PRF-119 demonstrated activity against all clinical S. aureus isolates collected from multiple centers in a European country (3), the present study aimed at challenging the optimized bacteriophage endolysin HY-133 with isolates belonging to the S. aureus complex from sub-Sahara Africa, including the recently described species Staphylococcus schweitzeri (5, 6). This species shows a peptidoglycan type which is distinct from that of S. aureus sensu stricto (5).Here, we tested the in vitro activity of HY-133 against a highly diverse collection of African S. aureus complex lineages (n ϭ 61). This collection consists of major African methicillin-susceptible S. aureus (MSSA), as well as methicillin-, ceftaroline/ceftobiprole-, and borderline oxacillin-resistant S. aureus from humans (colonization and infection) and animals (colonization) ( Table 1). The most common African MSSA and MRSA included in this study represent lineages which have been found to be predominant in sub-Saharan Africa based on a recent review (7). We also included 25 isolates from different clonal lineages of S. schweitzeri. The multilocus sequence types (ST) of the isolates included in this study are given in Table 1. The activity of HY-133 was determined using the broth microdilution method in accordance wi...

BackgroundRifampin-soaked synthetic prosthetic grafts have been widely used for prevention or treatment of vascular graft infections (VGIs).This in vitro study investigated the effect of the antibiotics daptomycin and vancomycin and the new recombinant bacteriophage endolysin HY-133 on vascular cells, as potential alternatives compared to rifampin.Material/MethodsPrimary human ECs, vascular smooth muscle cells (vSMC), and fibroblasts were cultivated in 96-well plates and incubated with rifampin, daptomycin, vancomycin, and endolysin HY-133 for 24 h. Subsequently, after washing, cell viability was determined by measuring mitochondrial ATP concentration. Antibiotics were used in their corresponding minimum and maximum serum concentrations, in decimal multiples and in maximum soaking concentration. The experiments were performed in triplicate.ResultsThe 10-fold max serum concentrations of rifampin, daptomycin, and vancomycin did not influence viability of EC and vSMC (100 μg/ml, p>0.170). Higher concentrations of rifampin (>1 mg/ml) significantly (p<0.001) reduced cell viability of all cell types. For the other antibiotics, high concentrations (close to maximum soaking concentration) were most cytotoxic for EC and vSMC and fibroblasts (p<0.001). Endolysin did not display any cytotoxicity towards vascular cells.ConclusionsResults of this in vitro study show the high cytotoxicity of rifampin against vascular cells, and may re-initiate the discussion about the benefit of prophylactic pre-soaking in high concentrations of rifampin. Further studies are necessary to determine the influence of rifampin on the restoration of vessel functionality versus its prophylactic effect against VGIs. Future use of recombinant phage endolysins for alternative prophylactic strategies needs further investigations.

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