An extraordinary dairy phage and its properties: occurrence, growth, inactivation, survival

Thermal and Chemical Inactivation of Bacillus Phage BM-P1

Bacillus spp. are often used as probiotics; however, they can be infected by phages, leading to significant economic losses. Biocidal and thermal treatments are considered rapid and effective methods for controlling microbial contamination. To prevent viral contamination in industrial dairy production, the impact of temperature and biocides on the viability of Bacillus methylotrophic phage BM-P1 was assessed. The results demonstrated that reconstituted skim milk (RSM) as a medium showed the most effective protective effect on phage BM-P1. Treatment at 90°C for 5 min or 72°C for 10 min inactivated it to nondetectable levels from the initial titer of 7.19 ± 0.11 log, regardless of the culture medium. Sodium hypochlorite exhibited the best inactivating effect, which could reduce the phage titer below the detection level in 4 min at 50 ppm. Additionally, treatment with 75% ethanol for 20 min or 50% isopropanol for 30 min could achieve inactivation to nondetectable levels. The inactivating effect of peracetic acid was limited; even when treated at the highest concentration (0.45%) for 60 min, only a 2.47 ± 0.17 log reduction was observed. This study may provide some theoretical basis and data support for establishing measures against Bacillus spp. phages.

An Overview of Diverse Strategies To Inactivate Enterobacteriaceae-Targeting Bacteriophages

Bacteriophages are viruses that infect bacteria and thus threaten industrial processes relying on the production executed by bacterial cells. Industries bear huge economic losses due to such recurring and resilient infections. Depending on the specificity of the process, there is a need for appropriate methods of bacteriophage inactivation, with an emphasis on being inexpensive and high efficiency. In this review, we summarize the reports on antiphagents, i.e., antibacteriophage agents on inactivation of bacteriophages. We focused on bacteriophages targeting the representatives of the Enterobacteriaceae family, as its representative, Escherichia coli, is most commonly used in the bio-industry. The review is divided into sections dealing with bacteriophage inactivation by physical factors, chemical factors, and nanotechnology-based solutions.

Does the high biodiversity of lactococcal bacteriophages allow predictions about their different UV-C susceptibilities?

Fermentation processes can only succeed if intact and active starter cultures are present. Bacteriophages, which can lyse bacteria and thus bring entire fermentation processes to a standstill, therefore pose a major threat. Cheese production, for example, is often affected. The by-product whey can be highly contaminated with bacteriophages (≤10⁹ plaque-forming units/mL) and in this state, further utilization is a quality and processing risk. Therefore, an orthogonal process consisting of membrane filtration followed by UV-C irradiation could be applied to eliminate bacteriophages and to generate "phage-free" whey. In order to define suitable process parameters, 11 lactococcal bacteriophages belonging to different families and genera and differing in their morphology, genome size, heat resistance, and other attributes, were screened for their UV-C resistance in whey. P369 was found to be the most resistant and could thus be well-suited as a biomarker. Starting from a 4 log unit bacteriophage reduction by membrane filtration, another 5 log unit decrease should be realized when applying a UV-C dose of 5 J/cm². A clear correlation of UV-C sensitivity to the chosen attributes studied such as bacteriophage morphology and genome size was difficult and ambiguous, presumably because other yet unidentified parameters are important. Mutation experiments were performed with the representative bacteriophage P008 by multiple cycles of UV-C irradiation and propagation. A few mutational events were found, but could not be linked to an artificially generated UV-C resistance, indicating that the process used would probably not lose its effectiveness over time.

Microencapsulation of Bacteriophages for the Delivery to and Modulation of the Human Gut Microbiota through Milk and Cereal Products

There is a bidirectional interaction between the gut microbiota and human health status. Disturbance of the microbiota increases the risk of pathogen infections and other diseases. The use of bacteriophages as antibacterial therapy or prophylaxis is intended to counteract intestinal disorders. To deliver bacteriophages unharmed into the gut, they must be protected from acidic conditions in the stomach. Therefore, an encapsulation method based on in situ complexation of alginate (2%), calcium ions (0.5%), and milk proteins (1%) by spray drying was investigated. Powdered capsules with particle sizes of ~10 µm and bacteriophage K5 titers of ~108 plaque forming units (pfu) g−1 were obtained. They protected the bacteriophages from acid (pH 2.5) in the stomach for 2 h and released them within 30 min under intestinal conditions (in vitro). There was no loss of viability during storage over two months (4 °C). Instead of consuming bacteriophage capsules in pure form (i.e., as powder/tablets), they could be inserted into food matrices, as exemplary shown in this study using cereal cookies as a semi-solid food matrix. By consuming bacteriophages in combination with probiotic organisms (e.g., via yoghurt with cereal cookies), probiotics could directly repopulate the niches generated by bacteriophages and, thus, contribute to a healthier life.