Long-circulating bacteriophage as antibacterial agents.

TLDR

The therapeutic use of phages as antibacterial agents has been limited by their narrow host range, the presence of toxins in crude lysates, and rapid clearance by the reticuloendothelial system. The study aimed to improve bacteriophage efficacy against multidrug‑resistant bacteria. The authors used strain‑specific virulent phages in bacteremic mice and applied serial passage to select mutants that persist longer in circulation. Purified phage preparations had lower toxin levels, and the serial‑passage approach produced long‑circulating lambda and P22 mutants that exhibited superior antibacterial activity in lethal infection models, with the mutation altering the major capsid protein E.

Abstract

The increased prevalence of multidrug-resistant bacterial pathogens motivated us to attempt to enhance the therapeutic efficacy of bacteriophages. The therapeutic application of phages as antibacterial agents was impeded by several factors: (i) the failure to recognize the relatively narrow host range of phages; (ii) the presence of toxins in crude phage lysates; and (iii) a lack of appreciation for the capacity of mammalian host defense systems, particularly the organs of the reticuloendothelial system, to remove phage particles from the circulatory system. In our studies involving bacteremic mice, the problem of the narrow host range of phage was dealt with by using selected bacterial strains and virulent phage specific for them. Toxin levels were diminished by purifying phage preparations. To reduce phage elimination by the host defense system, we developed a serial-passage technique in mice to select for phage mutants able to remain in the circulatory system for longer periods of time. By this approach we isolated long-circulating mutants of Escherichia coli phage lambda and of Salmonella typhimurium phage P22. We demonstrated that the long-circulating lambda mutants also have greater capability as antibacterial agents than the corresponding parental strain in animals infected with lethal doses of bacteria. Comparison of the parental and mutant lambda capsid proteins revealed that the relevant mutation altered the major phage head protein E. The use of toxin-free, bacteria-specific phage strains, combined with the serial-passage technique, may provide insights for developing phage into therapeutically effective antibacterial agents.