More Is Better: Selecting for Broad Host Range Bacteriophages

Abstract

Bacteriophages are viruses that infect bacteria. In this perspective, we discuss several aspects of a characteristic feature of bacteriophages, their host range. Each phage has its own particular host range, the range of bacteria that it can infect. While some phages can only infect one or a few bacterial strains, other phages can infect many species or even bacteria from different genera. Different methods for determining host range may give different results, reflecting the multiple mechanisms bacteria have to resist phage infection and reflecting the different steps of infection each method depends on. This makes defining host range difficult. Another difficulty in describing host range arises from the inconsistent use of the words “narrow” and especially “broad” when describing the breadth of the host range. Nearly all bacteriophages have been isolated using a single host strain of bacteria. While this procedure is fairly standard, it may more likely produce narrow rather than broad host range phage. Our results and those of others suggest that using multiple host strains during isolation can more reliably produce broader host range phages. This challenges the common belief that most bacteriophages have a narrow host range. We highlight the implications of this for several areas that are affected by host range including horizontal gene transfer and phage therapy.

Review article: bacteriophages in gastroenterology—from biology to clinical applications

“…Phages have different ranges of bacteria they can infect. Some phages are only able to infect a single or a small number of strains, while others can infect bacteria from different genera . These differences are determined by specific phage receptors present in the surface of the host cell (eg OmpC or lipopolysaccharide O‐antigen) …”

Phage therapy: awakening a sleeping giant

“…Another inherent feature of phages is that each has its own specificity toward bacteria, with some infecting only a few strains within a species, while others can infect many strains even across different related species [17]. This relatively narrow spectrum of individual phages can be assimilated into a tool that can very precisly remove only unwanted bacteria, in contrast with the blind action of antibiotics that kill many bacteria.…”

“…Conversely, even phages with the broadest bacterial spectrums still do not come close to those of broad-spectrum antimicrobials. However, phage narrow host ranges cannot be assumed to exist in nature [17]. For instance, nearly all therapeutic phages have been isolated and continually propagated using a single pathogenic strain.…”

“…Moreover, selection priority is largely given to those phages that rapidly kill this strain, before screening on an empirical collection of strains in vitro to determine host ranges. Modifying isolation procedures and growth conditions can favor the isolation of phages with much broader host ranges [17]. For example, phage Mu is polyvalent, making it able to infect species of Escherichia, Citrobacter, Shigella, Enterobacter, and Erwinia [17].…”

“…Modifying isolation procedures and growth conditions can favor the isolation of phages with much broader host ranges [17]. For example, phage Mu is polyvalent, making it able to infect species of Escherichia, Citrobacter, Shigella, Enterobacter, and Erwinia [17]. Moreover, over 700 strains of Staphylococcus aureus can be lysed by a single phage [21].…”