Salmonella Host Range of Bacteriophages That Infect Multiple Genera

161

130

Salmonella enterica and Escherichia coli O157:H7 are major food-borne pathogens causing serious illness. Phage SFP10, which revealed effective infection of both S. enterica and E. coli O157:H7, was isolated and characterized. SFP10 contains a 158-kb double-stranded DNA genome belonging to the Vi01 phage-like family Myoviridae. In vitro adsorption assays showed that the adsorption constant rates to both Salmonella enterica serovar Typhimurium and E. coli O157:H7 were 2.50 ؋ 10 ؊8 ml/min and 1.91 ؋ 10 ؊8 ml/min, respectively. One-step growth analysis revealed that SFP10 has a shorter latent period (25 min) and a larger burst size (>200 PFU) than ordinary Myoviridae phages, suggesting effective host infection and lytic activity. However, differential development of resistance to SFP10 in S. Typhimurium and E. coli O157:H7 was observed; bacteriophage-insensitive mutant (BIM) frequencies of 1.19 ؋ 10 ؊2 CFU/ml for S. Typhimurium and 4.58 ؋ 10 ؊5 CFU/ml for E. coli O157:H7 were found, indicating that SFP10 should be active and stable for control of E. coli O157:H7 with minimal emergence of SFP10-resistant pathogens but may not be for S. Typhimurium. Specific mutation of rfaL in S. Typhimurium and E. coli O157:H7 revealed the O antigen as an SFP10 receptor for both bacteria. Genome sequence analysis of SFP10 and its comparative analysis with homologous Salmonella Vi01 and Shigella phiSboM-AG3 phages revealed that their tail fiber and tail spike genes share low sequence identity, implying that the genes are major host specificity determinants. This is the first report identifying specific infection and inhibition of Salmonella Typhimurium and E. coli O157:H7 by a single bacteriophage.

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Characterization and Comparative Genomic Analysis of a Novel Bacteriophage, SFP10, Simultaneously Inhibiting both Salmonella enterica and Escherichia coli O157:H7

Park

Lee

Shin

et al. 2012

161

130

“…However, their broad-host-range properties were discovered accidently, and few studies have explored methods for isolating and enriching polyvalent phages. Jensen et al developed a multiple-host enrichment method to identify phages capable of interclass infectivity (13), and Bielke et al used a sequential isolation method to isolate phages with intergenus infectivity (14). However, these phage isolation methods have yielded variable results, with a later experiment showing no significant difference in phage host range (15).…”

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confidence: 99%

Isolation of Polyvalent Bacteriophages by Sequential Multiple-Host Approaches

Mathieu

et al. 2016

111

126

Many studies on phage biology are based on isolation methods that may inadvertently select for narrow-host-range phages. Consequently, broad-host-range phages, whose ecological significance is largely unexplored, are consistently overlooked. To enhance research on such polyvalent phages, we developed two sequential multihost isolation methods and tested both culturedependent and culture-independent phage libraries for broad infectivity. Lytic phages isolated from activated sludge were capable of interspecies or even interorder infectivity without a significant reduction in the efficiency of plating (0.45 to 1.15). Two polyvalent phages (PX1 of the Podoviridae family and PEf1 of the Siphoviridae family) were characterized in terms of adsorption rate (3.54 ؋ 10 ؊10 to 8.53 ؋ 10 ؊10 ml/min), latent time (40 to 55 min), and burst size (45 to 99 PFU/cell), using different hosts. These phages were enriched with a nonpathogenic host (Pseudomonas putida F1 or Escherichia coli K-12) and subsequently used to infect model problematic bacteria. By using a multiplicity of infection of 10 in bacterial challenge tests, >60% lethality was observed for Pseudomonas aeruginosa relative to uninfected controls. The corresponding lethality for Pseudomonas syringae was ϳ50%. Overall, this work suggests that polyvalent phages may be readily isolated from the environment by using different sequential hosts, and this approach should facilitate the study of their ecological significance as well as enable novel applications.T he total bacteriophage (phage) population on Earth is estimated at 10 31 or more, making phages by far the most abundant biological entities on the planet (1, 2). As such, phages exert a significant influence over global biogeochemical cycles (3, 4) and are important drivers of bacterial diversity (5). Considering their ecological importance and value as a potential genetic resource, increasing our fundamental understanding of phage biology may facilitate the development of novel applications. However, research on phage diversity and ecology may be inadvertently limited by the use of biased isolation techniques that preferentially select for narrow-host-range phages (6, 7), while-broad hostrange phages are consistently overlooked.The classic approach to isolate and study phages is typically performed with high-density, nutrient-rich batch monocultures grown under planktonic conditions and most often results in the isolation of narrow-host-range phages (8)(9)(10).Previous studies have demonstrated the existence of polyvalent phages, among which the temperate phages P1 and Mu are the most studied (11, 12). However, their broad-host-range properties were discovered accidently, and few studies have explored methods for isolating and enriching polyvalent phages. Jensen et al. developed a multiple-host enrichment method to identify phages capable of interclass infectivity (13), and Bielke et al. used a sequential isolation method to isolate phages with intergenus infectivity (14). However, these phage isolation methods have...

“…The high host specificity of most phages is a double-edged sword; high specificity is necessary for the specific targeting of unwanted bacteria, but the narrow host range renders phage biocontrol ineffective for non-host strains (22). The use of broad-hostrange phages isolated by multiple-host enrichment methods (7,11,29) or a phage cocktail composed of multiple phage types (33,44,55) has shown promise in overcoming this problem. Another limitation is the rapid emergence of phage-resistant mutants (6,11,18,32).…”

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confidence: 99%

Characterization of a T5-Like Coliphage, SPC35, and Differential Development of Resistance to SPC35 in Salmonella enterica Serovar Typhimurium and Escherichia coli

Kim

Ryu

2011

103

106

The potential of bacteriophage as an alternative biocontrol agent has recently been revisited due to the widespread occurrence of antibiotic-resistant bacteria. We isolated a virulent bacteriophage, SPC35, that can infect both Salmonella enterica serovar Typhimurium and Escherichia coli. Morphological analysis by transmission electron microscopy and analysis of its 118,351-bp genome revealed that SPC35 is a T5 group phage belonging to the family Siphoviridae. BtuB, the outer membrane protein for vitamin B 12 uptake, was found to be a host receptor for SPC35. Interestingly, resistant mutants of both E. coli and S. Typhimurium developed faster than our expectation when the cultures were infected with SPC35. Investigation of the btuB gene revealed that it was disrupted by the IS2 insertion sequence element in most of the resistant E. coli isolates. In contrast, we could not detect any btuB gene mutations in the resistant S. Typhimurium isolates; these isolates easily regained sensitivity to SPC35 in its absence, suggesting phase-variable phage resistance/sensitivity. These results indicate that a cocktail of phages that target different receptors on the pathogen should be more effective for successful biocontrol.