Don’t Shut the Stable Door after the Phage Has Bolted—The Importance of Bacteriophage Inactivation in Food Environments

In recent years, a new potential measure against foodborne pathogenic bacteria was rediscovered—bacteriophages. However, despite all their advantages, in connection to their widespread application in the food industry, negative consequences such as an uncontrolled phage spread as well as a development of phage resistant bacteria can occur. These problems are mostly a result of long-term persistence of phages in the food production environment. As this topic has been neglected so far, this article reviews the current knowledge regarding the effectiveness of disinfectant strategies for phage inactivation and removal. For this purpose, the main commercial phage products, as well as their application fields are first discussed in terms of applicable inactivation strategies and legal regulations. Secondly, an overview of the effectiveness of disinfectants for bacteriophage inactivation in general and commercial phages in particular is given. Finally, this review outlines a possible strategy for users of commercial phage products in order to improve the effectiveness of phage inactivation and removal after application.

Persistence of Infectious Shiga Toxin-Encoding Bacteriophages after Disinfection Treatments

ABSTRACTIn Shiga toxin-producingEscherichia coli(STEC), induction of Shiga toxin-encoding bacteriophages (Stx phages) causes the release of free phages that can later be found in the environment. The ability of Stx phages to survive different inactivation conditions determines their prevalence in the environment, the risk ofstxtransduction, and the generation of new STEC strains. We evaluated the infectivity and genomes of two Stx phages (Φ534 and Φ557) under different conditions. Infectious Stx phages were stable at 4, 22, and 37°C and at pH 7 and 9 after 1 month of storage but were completely inactivated at pH 3. Infective Stx phages decreased moderately when treated with UV (2.2-log10reduction for an estimated UV dose of 178.2 mJ/cm2) or after treatment at 60 and 68°C for 60 min (2.2- and 2.5-log10reductions, respectively) and were highly inactivated (3 log10) by 10 ppm of chlorine in 1 min. Assays in a mesocosm showed lower inactivation of all microorganisms in winter than in summer. The number of Stx phage genomes did not decrease significantly in most cases, and STEC inactivation was higher than phage inactivation under all conditions. Moreover, Stx phages retained the ability to lysogenizeE. coliafter some of the treatments.

Control of Bacterial Seedling Rot and Seedling Blight of Rice by Bacteriophage

In Japan, rice seed are immersed in pesticide solutions to prevent seedborne diseases that attack greenhouse seedlings. However, disposal of large quantities of waste pesticide solutions after treatment is costly. As an alternative treatment, bacteriophages (phages) that are highly specific to the target bacteria are considered as potential biocontrol agents. Here, we isolated three phage strains that lyse Burkholderia glumae and B. plantarii, the causative pathogens of seedling rot and seedling blight, respectively. Two phages could lyse both bacteria and clearly suppress these diseases. One of these phages (BGPP-Ar) suppressed these diseases more effectively than existing pesticides: the ratio of seedlings exhibiting disease to the total number of seedlings examined after treatment with BGPP-Ar 1.0 × 108 plaque-forming units (PFU)/ml was 0.0 for seedling rot and 2.0 for seedling blight; after treatment with ipconazole/copper (II) hydroxide, the ratios were 14.3 and 15.0, respectively. BGPP-Ar was highly effective in suppressing seedling rot of rice, even at the low concentration of 1.0 × 105 PFU/ml. The best phage treatment effect for sterilizing seed is achieved indoors to avoid phage inactivation by UV irradiation. Treatment effect was demonstrated on seed infected with pathogens. Therefore, we consider that phage treatment was effective in this study.

Molecular Interaction between Lipoteichoic Acids and Lactobacillus delbrueckii Phages Depends on d-Alanyl and α-Glucose Substitution of Poly(Glycerophosphate) Backbones

ABSTRACT Lipoteichoic acids (LTAs) have been shown to act as bacterial counterparts to the receptor binding proteins of LL-H, LL-H host range mutant LL-H-a21, and JCL1032. Here we have used LTAs purified by hydrophobic interaction chromatography from different phage-resistant and -sensitive strains of Lactobacillus delbrueckii subsp. lactis. Nuclear magnetic resonance analyses revealed variation in the degree of α-glucosyl and d-alanyl substitution of the 1,3-linked poly(glycerophosphate) LTAs between the phage-sensitive and phage-resistant strains. Inactivation of phages was less effective if there was a high level of d-alanine residues in the LTA backbones. Prior incubation of the LTAs with α-glucose-specific lectin inhibited the LL-H phage inactivation. The overall level of decoration or the specific spatial combination of α-glucosyl-substituted, d-alanyl-substituted, and nonsubstituted glycerol residues may also affect phage adsorption.