Abstract
Some bacterial strains of the multidrug-resistant Gram-positive bacteria Enterococcus faecalis can significantly reduce the efficacy of conventional antimicrobial chemotherapy. Thus, the introduction of bacteriophage (phage) therapy is expected, where a phage is used as a bioagent to destroy bacteria. E. faecalis phage ΦEF24C is known to be a good candidate for a therapeutic phage against E. faecalis. However, this therapeutic phage still produces nonuniform antimicrobial effects with different bacterial strains of the same species and this might prove detrimental to its therapeutic effects. One solution to this problem is the preparation of mutant phages with higher activity, based on a scientific rationale. This study isolated and analyzed a spontaneous mutant phage, ΦEF24C-P2, which exhibited higher infectivity against various bacterial strains when compared with phage ΦEF24C. First, the improved bactericidal effects of phage ΦEF24C-P2 were attributable to its increased adsorption rate. Moreover, genomic sequence scanning revealed that phage ΦEF24C-P2 had a point mutation in orf31. Proteomic analysis showed that ORF31 (mw, 203 kDa) was present in structural components, and immunological analysis using rabbit-derived antibodies showed that it was a component of a long, flexible fine tail fiber extending from the tail end. Finally, phage ΦEF24C-P2 also showed higher bactericidal activity in human blood compared with phage ΦEF24C using the in vitro assay system. In conclusion, the therapeutic effects of phage ΦEF24C-P2 were improved by a point mutation in gene orf31, which encoded a tail fiber component.
Highlights
IntroductionVancomycinresistant Enterococcus (VRE) species are medically important because they fail to respond to conventional antimicrobial chemotherapy and cause fatal infections in nosocomial settings
Phage WEF24C was plated onto E. faecalis strain VRE2 and a large-plaque-forming spontaneous mutant phage WEF24C-P2 was isolated (Figure 1)
Phage infectivity with various bacterial strains was evaluated by comparing the efficiency of plating (EOP) of the wild-type phage WEF24C and the mutant phage WEF24C-P2
Summary
Vancomycinresistant Enterococcus (VRE) species are medically important because they fail to respond to conventional antimicrobial chemotherapy and cause fatal infections in nosocomial settings. The situation is critical, antimicrobial agents with new modes of action are unlikely to be developed because there is little commercial interest in producing novel antibiotics or in developing novel technology [7,8]. To combat this bacterium, an alternative therapeutic approach to antibiotics must be explored. One of the favored alternative therapies to antibiotics is phage therapy, which uses bacteriophages (bacterial viruses) as selective bioagents to destroy the targeted bacteria
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