Recent advances in viral metagenomics have enabled the rapid discovery of an unprecedented catalogue of phages in many biomes. While it significantly expanded our understanding of how

Bacteriophage (phage) therapy, i.e., the use of viruses that infect bacteria as antimicrobial agents, is a promising alternative to conventional antibiotics. Indeed, resistance to antibiotics has become a major public health problem after decades of extensive usage. However, one of the main questions regarding phage therapy is the possible rapid emergence of phage-resistant bacterial variants, which could impede favourable treatment outcomes. Experimental data has shown that phage-resistant variants occurred in up to 80% of studies targeting the intestinal milieu and 50% of studies using sepsis models. Phage-resistant variants have also been observed in human studies, as described in three out of four clinical trials that recorded the emergence of phage resistance. On the other hand, recent animal studies suggest that bacterial mutations that confer phage-resistance may result in fitness costs in the resistant bacterium, which, in turn, could benefit the host. Thus, phage resistance should not be underestimated and efforts should be made to develop methodologies for monitoring and preventing it. Moreover, understanding and taking advantage of the resistance-induced fitness costs in bacterial pathogens is a potentially promising avenue.

Background.Increasing antibiotic resistance warrants therapeutic alternatives. Here we investigated the efficacy of bacteriophage-therapy (phage) alone or combined with antibiotics against experimental endocarditis (EE) due to Pseudomonas aeruginosa, an archetype of difficult-to-treat infection.Methods.In vitro fibrin clots and rats with aortic EE were treated with an antipseudomonas phage cocktail alone or combined with ciprofloxacin. Phage pharmacology, therapeutic efficacy, and resistance were determined.Results.In vitro, single-dose phage therapy killed 7 log colony-forming units (CFUs)/g of fibrin clots in 6 hours. Phage-resistant mutants regrew after 24 hours but were prevented by combination with ciprofloxacin (2.5 × minimum inhibitory concentration). In vivo, single-dose phage therapy killed 2.5 log CFUs/g of vegetations in 6 hours (P < .001 vs untreated controls) and was comparable with ciprofloxacin monotherapy. Moreover, phage/ciprofloxacin combinations were highly synergistic, killing >6 log CFUs/g of vegetations in 6 hours and successfully treating 64% (n = 7/11) of rats. Phage-resistant mutants emerged in vitro but not in vivo, most likely because resistant mutations affected bacterial surface determinants important for infectivity (eg, the pilT and galU genes involved in pilus motility and LPS formation).Conclusions.Single-dose phage therapy was active against P. aeruginosa EE and highly synergistic with ciprofloxacin. Phage-resistant mutants had impaired infectivity. Phage-therapy alone or combined with antibiotics merits further clinical consideration.

Bacteriophage therapy is a commonly used treatment for Staphylococcus aureus infections in countries of the former Soviet Union, using both single phages and phage cocktails. The scarce data available on Eastern phage cocktails prompted an investigation into commercially-available Pyophage cocktails from two different manufacturers used to treat skin and wound infections. Comparison of the metagenomic composition of two Pyophage products from Georgia and Russia revealed substantial differences in phage-types targeting Escherichia, Enterococcus, Salmonella, Pseudomonas aeruginosa and Proteus, therefore indicating multiple strategies for composing phage cocktails against these bacterial pathogens. Closely-related Kayvirus-like Myoviruses were, however, a shared component against S. aureus within all products, except for the inclusion of a secondary S. aureus Podovirus in one Microgen cocktail. Metagenomic analysis also revealed the presence of several probable prophage sequences but detected no genetic safety risks in terms of virulence factors or antibiotic resistance genes. The safety of broad-spectrum cocktails was tested by comparing the effects of nasal and oral exposure to Eliava Pyophage, a monospecies counterpart and placebo in healthy human carriers of S. aureus. The lack of adverse effects in any treatment groups supports the clinical safety of S. aureus phages administered as a single phage or as phage cocktail.

The recent rise of multidrug-resistant Gram-negative bacteria represents a serious threat to public health and makes the search for novel effective alternatives to antibiotics a compelling need. Bacteriophage (Phage) lysins are enzymes that hydrolyze the cell wall of bacteria and represent a promising alternative to tackle this ever-increasing problem. Despite their use is believed to be restricted to Gram-positive bacteria, recent findings have shown that they can also be used against Gram-negative bacteria. By using a phage genome-based screening approach, we identified and characterized a novel lysin, PlyE146, encoded by an Escherichia coli prophage and with a predicted molecular mass of ca. 17 kDa. PlyE146 is composed of a C-terminal cationic peptide and a N-terminal N-acetylmuramidase domain. Histidine-tagged PlyE146 was overexpressed from a plasmid in Lactococcus lactis NZ9000 and purified by NI-NTA chromatography. PlyE146 exhibited in vitro optimal bactericidal activity against E. coli K12 (3.6 log10 CFU/mL decrease) after 2 h of incubation at 37°C at a concentration of 400 μg/mL in the absence of NaCl and at pH 6.0. Under these conditions, PlyE146 displayed antimicrobial activity towards several other E. coli, Pseudomonas aeruginosa (3 to 3.8-log10 CFU/mL decrease) and Acinetobacter baumannii (4.9 to >5-log10 CFU/mL decrease) strains. Therefore, PlyE146 represents a promising therapeutic agent against E. coli, P. aeruginosa and A. baumannii infections. However, further studies are required to improve the efficacy of PlyE146 under physiological conditions.