Resistance of two temperate Lactobacillus paracasei bacteriophages to high pressure homogenization, thermal treatments and chemical biocides of industrial application

Inactivation of Lactobacillus Bacteriophages by Dual Chemical Treatments

Phage contamination is one of the significant problems in the food fermentation industry, which eventually causes economic losses to the industry. Here, we investigated the viability of Lactobacillus plantarum phage P1 and P2 using various biocides treatments (ethanol, isopropanol, sodium hypochlorite and peracetic acid). Results indicated that phage P1 and P2 could be completely inactivated by treatment with 75% ethanol for 5 min, followed by 400 ppm of sodium hypochlorite treatment for 5 min. Phage P2 could be completely inactivated in the reverse sequence, while 800 ppm of sodium hypochlorite was required to achieve a similar effect for phage P1. Moreover, 100% isopropanol could increase the inactivating effect of 75% ethanol. This study may provide basic information on using multiple antimicrobials for phage control in laboratories and food plants.

How to Tackle Bacteriophages: The Review of Approaches with Mechanistic Insight

Bacteriophage-based applications have a renaissance today, increasingly marking their use in industry, medicine, food processing, biotechnology, and more. However, phages are considered resistant to various harsh environmental conditions; besides, they are characterized by high intra-group variability. Phage-related contaminations may therefore pose new challenges in the future due to the wider use of phages in industry and health care. Therefore, in this review, we summarize the current knowledge of bacteriophage disinfection methods, as well as highlight new technologies and approaches. We discuss the need for systematic solutions to improve bacteriophage control, taking into account their structural and environmental diversity.

Lytic bacteriophages UFJF_PfDIW6 and UFJF_PfSW6 prevent Pseudomonas fluorescens growth in vitro and the proteolytic-caused spoilage of raw milk during chilled storage

In this study, P. fluorescens-infecting phages were isolated, characterized, and evaluated to their potential to control the bacterial counts and, consequently, the proteolytic spoilage of raw milk during cold storage. The UFJF_PfDIW6 and UFJF_PfSW6 phages showed titers of 9.7 and 7.6 log PFU/ml; latent period of 115 and 25 min, and burst size of 145 and 25 PFU/infected cell, respectively. They also were highly specific to the host bacterium, morphologically classified as the Podoviridae family, stable at pH 5 to 11 and were not inactivated at 63 °C or 72 °C for 30 min. These phages found to be effective against P. fluorescens, reducing bacterial count throughout the entire exponential growth phase in broth formulated with milk at both 4 °C and 10 °C. This effect on bacteria growth led to inhibition by at least 2 days in proteases production, delaying the degradation of milk proteins. When applied together in raw milk stored at 4 °C, they reduced the total bacteria, psychrotrophic, and Pseudomonas by 3 log CFU/ml. This study's findings indicate that these phages have a great potential to prevent the growth of Pseudomonas and, consequently, to retard proteolytic spoilage of raw milk during chilled storage.

Bacteriophages in dairy plants

Bacteriophages represent the main microbiological threat for the manufacture of fermented foods. The dairy industry is the most affected by this problem, as phages are naturally present in raw milk, surfaces, vats, tanks, floors, and distributed by air displacements. Cheese whey may also contain high phage concentrations. Prophages harbored by lysogenic strains could be induced, generating new lytic phages. In this context, where phages cannot be eradicated from dairies, methods of phage monitoring are mandatory. These are mainly based in microbiological features, like classical methods, that are the most used, economic and simple to carry out. Phage DNA detection and quantification by PCR and qPCR, more complex and expensive, are faster, although not able to discern between viable and non-viable virions. Electron microscopy allows direct visualization and characterization of phage morphology, but the apparatus is expensive. Alternative methods based in other phage traits also exist, though less studied and not applicable on a daily basis. Recognition of contamination sources and correct phage monitoring in dairy factories allow a correct application of control measures. These include general measures such as proper factory design, efficient programs of sanitization, good treatment of raw materials, especially milk, and careful handling of by-products. Additionally, the use of starts cultures should be adequate, with application of rotation schemes when possible. Finally, the selection of bacteriophage insensitive mutants (BIM) is essential, and can be achieved simply and empirically, though the study of CRISPR-Cas and other newly discovered mechanisms provide a more rational basis to obtain BIMs with optimized features.

Inactivation of Dairy Bacteriophages by Thermal and Chemical Treatments

This article provides information on the characteristics of diverse phages of lactic acid bacteria and highlights the incidence of their presence in different dairy fermentations. As it is known, thermal treatments on raw milk and use of sanitizers in the disinfection of surfaces and equipment are strategies usually applied in dairy to prevent bacteriophage infections. In this sense, this review mainly focuses on the existing data about the resistance against thermal treatments and sanitizers usually used in the dairy industry worldwide, and the differences found among bacteriophages of diverse genera are remarked upon. Also, we provide information concerning the problems that have arisen as a consequence of the potential presence of bacteriophages in cheese whey powder and derivatives when they are added in fermented dairy product manufacturing. Finally, some important conclusions on each topic are marked and checkpoints to be considered are suggested.

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.

Inactivation of Lactobacillus Virulent Bacteriophage by Thermal and Chemical Treatments

The uses of thermal and chemical treatments were evaluated with respect to the inactivation of the Lactobacillus virulent bacteriophage P2. Thermal treatments consisted of heating the phage at 63, 72, and 90°C in three broth media: de Man Rogosa Sharpe broth, reconstituted skim milk, and Tris magnesium gelatin buffer. Chemical treatments evaluated were ethanol, isopropanol, sodium hypochlorite, and peracetic acid at various concentrations. Phage P2 was completely inactivated in 20 and 5 min at 72 and 90°C, respectively. Reconstituted skim milk and de Man Rogosa Sharpe broth provided optimum and minimum heat protection, respectively. Only sodium hypochlorite at 400 and 800 ppm completely inactivated the phage in 50 and 30 min, respectively. Treatment with 100% ethanol and isopropanol resulted in only a ca. 5.1-log reduction. Peracetic acid at the highest concentration used (0.45%) resulted in only a 1.40-log reduction of the phage within 60 min. These results provide additional data for establishing effective methods of controlling phage contamination in dairy and laboratory environments.

Bacteriophages on dairy foods

This review focuses on the impact of bacteriophages on the manufacture of dairy foods. Firstly, the impact of phages of lactic acid bacteria in the dairy industry, where they are considered enemies, is discussed. The sources of phage contamination in dairy plants are detailed, with special emphasis on the rise of phage infections related to the growing use of cheese whey as ingredient. Other topics include traditional and new methods of phage detection, quantification and monitoring, and strategies of phage control in dairy plants, either of physical, chemical or biological nature. Finally, the use of phages or purified phage enzymes as allies to control pathogenic bacteria in the food industry is reviewed.

New semi-pilot-scale reactor to study the photocatalytic inactivation of phages contained in aerosol

The aims of this work were to design and build a photocatalytic reactor (UV-A/TiO₂) to study the inactivation of phages contained in bioaerosols, which constitute the main dissemination via phages in industrial environments. The reactor is a close system with recirculation that consists of a stainless steel camera (cubic form, side of 60 cm) in which air containing the phage particles circulates and an acrylic compartment with six borosilicate plates covered with TiO₂. The reactor is externally illuminated by 20 UV-A lamps. Both compartments are connected by a fan to facilitate the sample circulation. Samples are injected into the camera using two piston nebulizers working in series whereas several methodologies for sampling (impinger/syringe, sampling on photocatalytic plates, and impact of air on slide) were assayed. The reactor setup was carried out using phage B1 (Lactobacillus plantarum), and assays demonstrated a decrease of phage counts of 2.7 log orders after 1 h of photocatalytic treatment. Photonic efficiencies of inactivation were assessed by phage sampling on the photocatalytic plates or by impact of air on a glass slide at the photocatalytic reactor exit. Efficiencies of the same order of magnitude were observed using both sampling methods. This study demonstrated that the designed photocatalytic reactor is effective to inactivate phage B1 (Lb. plantarum) contained in bioaerosols.

Phage Therapy: Beyond Antibacterial Action

Until recently, phages were considered as mere “bacteria eaters” with potential for use in combating antimicrobial resistance. The real value of phage therapy assessed according to the standards of evidence-based medicine awaits confirmation by clinical trials. However, the progress in research on phage biology has shed more light on the significance of phages. Accumulating data indicate that phages may also interact with eukaryotic cells. How such interactions could be translated into advances in medicine (especially novel means of therapy) is discussed herein.

Thermal-Stability and Reconstitution Ability of Listeria Phages P100 and A511

The study evaluated the thermal-stability of Listeria phages P100 and A511 at temperatures simulating the preparation of ready-to-eat meats. The phage infectivity after heating to 71°C and holding for a minimum of 30 s, before eventually cooling to 4°C were examined. Higher temperatures of 75, 80, and 85°C were also tested to evaluate their effect on phages thermal-stability. This study found that despite minor differences in the amino acid sequences of their structural proteins, the two phages responded differently to high temperatures. P100 activity declined at least 10 log (PFU mL-1) with exposure to 71°C (30 s) and falling below the limit of detection (1 log PFU mL-1) while, A511 dropped from 108 to 105 PFU mL-1. Cooling resulted in partial reconstitution of P100 phage particles to 103 PFU mL-1. Exposure to 75°C (30 s) abolished A511 activity (8 log PFU mL-1) and both phages showed reconstitution during cooling phase after exposure to 75°C. P100 exhibited reconstitution after treatment at 80°C (30 s), conversely A511 showed no reconstitution activity. Heating P100 to 85°C abolished the reconstitution potential. Substantial differences were found in thermal-stability and reconstitution of the examined phages showing A511 to be more thermo-stable than P100, while P100 exhibited reconstitution during cooling after treatment at 80°C which was absent in A511. The differences in predicted melting temperatures of structural proteins of P100 and A511 were consistent with the observed differences in thermal stability and morphological changes observed with transmission electron microscopy.

A fast PCR-based method for the characterization of prophage profiles in strains of the Lactobacillus casei group

Lysogeny is widespread among Lactobacillus strains of the casei group (L. casei, L. paracasei and L. rhamnosus), and prophages account for most strain-specific DNA. Numerous PCR based methods have been developed to detect free phages of lactic acid bacteria, but they do not take in consideration prophages. In this study, a new PCR method for the detection of lysogeny was developed using genome sequences of L. casei group strains (including BL23) and bacteriophages. Nine pairs of primers were designed to selectively amplify the highly conserved prophage iA2 (pairs #1-#3) and fragments of two groups phages of temperate origin: C_L1/C_L2/iLp1308/iLp84 (pairs #4 and #5) and Lrm1/J-1/PL-1/A2/AT3/Lc-Nu (pairs #6 to #9). Forty-nine strains of the casei group were subjected to PCR. Strains containing remnants of lytic phages outnumbered those containing iA2-related prophages. The combination of pair #2, annealing on the terminase large subunit (TLS), and pair #3, annealing on the helicase (forward) and a non-coding region (reverse), showed the best diagnostic performance for iA2-like prophages. For the assessment of remnants of phages C_L1/C_L2/iLp1308/iLp84, pair #4 (annealing on the TLS) was preferred over pair #5 (portal protein). Detection of phages Lrm1/J-1/PL-1/A2/AT3/Lc-Nu was optimal with primers of pair #6, designed on non-coding regions of phage genomes; pair #6 also evidenced a high conservation of certain prophage remnants. Overall, our PCR-based method successfully detected and discriminated groups of prophages or remnants in L. casei group strains.

Thermal and chemical inactivation of Lactobacillus virulent bacteriophage

The effect of thermal treatments and several biocides on the viability of Lactobacillus virulent phage P1 was evaluated. Times to achieve 99% inactivation (T₉₉) of phage at different treatment conditions were calculated. The thermal treatments applied were 63, 72, and 90°C in 3 suspension media (de Man, Rogosa, Sharpe broth, reconstituted skim milk, and Tris magnesium gelatin buffer). Phage P1 was completely inactivated in 5 and 10 min at 90 and 72°C, respectively; however, reconstituted skim milk provided better thermal protection at 63°C. When phage P1 was treated with various biocides, 800 mg/L of sodium hypochlorite was required for total inactivation (∼7.3 log reduction) within 60 min, whereas treatment with 100% ethanol resulted in only a ∼4.7 log reduction, and 100% isopropanol resulted in a 5.2-log reduction. Peracetic acid (peroxyacetic acid) at the highest concentration used (0.45%) resulted in only a ∼4.-log reduction of phage within 60 min. The results of this study provide additional information on effective treatments for the eradication of potential phage infections in dairy plants.

Biocidal Inactivation of Lactococcus lactis Bacteriophages: Efficacy and Targets of Commonly Used Sanitizers

Lactococcus lactis strains, being intensely used in the dairy industry, are particularly vulnerable to members of the so-called 936 group of phages. Sanitization and disinfection using purpose-made biocidal solutions is a critical step in controlling phage contamination in such dairy processing plants. The susceptibility of 36 936 group phages to biocidal treatments was examined using 14 biocides and commercially available sanitizers. The targets of a number of these biocides were investigated by means of electron microscopic and proteomic analyses. The results from this study highlight significant variations in phage resistance to biocides among 936 phages. Furthermore, rather than possessing resistance to specific biocides or biocide types, biocide-resistant phages tend to possess a broad tolerance to multiple classes of antimicrobial compounds.

The Survival of a Temperate vtx Bacteriophage and an Anti-Verocytotoxigenic Escherichia coli O157 Lytic Phage in Water and Soil Samples

Verocytotoxigenic (vtx) Escherichia coli (VTEC) are zoonotic foodborne pathogens with the vtx operon encoded by lambdoid bacteriophage (phage). Despite much research on the host bacteria, similar data on the persistence of verocytotoxin converting phage and the ecological niches where transduction occurs are lacking and novel VTEC of important public health significance, have and continue to emerge. This study investigated the survival of a temperate vtx bacteriophage (24_B ::kanamycin^R ) in water (raw farm, pasteurized farm, laboratory tap and autoclaved purified water) and soil (sandy loam and loam soil). It also examined the persistence of an anti-VTEC lytic phage (e11/2) in the same matrices as this may be one option for controlling the emergence of novel VTEC, especially in farm ecological niches where other control options, such as chemical, heat or high pressure treatments, are not feasible. Samples inoculated with 24_B ::kanamycin^R and e11/2 bacteriophage (8 log₁₀ pfu/ml or pfu/g) separately were incubated at 4°C and 14°C, representative Irish Winter and Summer temperatures, respectively, and tested every 2 days for 40 days. The transduction of 24_B ::kanamycin^R was also continuously assessed. Both phages survived with reductions observed, regardless of matrix or storage temperature. Moreover, 24_B ::kanamycin^R was able to transduce its host E. coli strain. It was therefore concluded that aquatic and soil environments on farms may serve as a vtx phage reservoir and transduction point but anti-VTEC phage is a possible biocontrol option.

Characterization, Genome Sequence, and Analysis of Escherichia Phage CICC 80001, a Bacteriophage Infecting an Efficient L-Aspartic Acid Producing Escherichia coli

Escherichia phage CICC 80001 was isolated from the bacteriophage contaminated medium of an Escherichia coli strain HY-05C (CICC 11022S) which could produce L-aspartic acid. The phage had a head diameter of 45-50 nm and a tail of about 10 nm. The one-step growth curve showed a latent period of 10 min and a rise period of about 20 min. The average burst size was about 198 phage particles per infected cell. Tests were conducted on the plaques, multiplicity of infection, and host range. The genome of CICC 80001 was sequenced with a length of 38,810 bp, and annotated. The key proteins leading to host-cell lysis were phylogenetically analyzed. One protein belonged to class II holin, and the other two belonged to the endopeptidase family and N-acetylmuramoyl-L-alanine amidase family, respectively. The genome showed the sequence identity of 82.7% with that of Enterobacteria phage T7, and carried ten unique open reading frames. The bacteriophage resistant E. coli strain designated CICC 11021S was breeding and its L-aspartase activity was 84.4% of that of CICC 11022S.

Bacteriophages Isolated from Chicken Meat and the Horizontal Transfer of Antimicrobial Resistance Genes

Antimicrobial resistance in microbes poses a global and increasing threat to public health. The horizontal transfer of antimicrobial resistance genes was thought to be due largely to conjugative plasmids or transposons, with only a minor part being played by transduction through bacteriophages. However, whole-genome sequencing has recently shown that the latter mechanism could be highly important in the exchange of antimicrobial resistance genes between microorganisms and environments. The transfer of antimicrobial resistance genes by phages could underlie the origin of resistant bacteria found in food. We show that chicken meat carries a number of phages capable of transferring antimicrobial resistance. Of 243 phages randomly isolated from chicken meat, about a quarter (24.7%) were able to transduce resistance to one or more of the five antimicrobials tested into Escherichia coli ATCC 13706 (DSM 12242). Resistance to kanamycin was transduced the most often, followed by that to chloramphenicol, with four phages transducing tetracycline resistance and three transducing ampicillin resistance. Phages able to transduce antimicrobial resistance were isolated from 44% of the samples of chicken meat that we tested. The statistically significant (P = 0.01) relationship between the presence of phages transducing kanamycin resistance and E. coli isolates resistant to this antibiotic suggests that transduction may be an important mechanism for transferring kanamycin resistance to E. coli. It appears that the transduction of resistance to certain antimicrobials, e.g., kanamycin, not only is widely distributed in E. coli isolates found on meat but also could represent a major mechanism for resistance transfer. The result is of high importance for animal and human health.

Bacteriophages Isolated from Chicken Meat and the Horizontal Transfer of Antimicrobial Resistance Genes

Antimicrobial resistance in microbes poses a global and increasing threat to public health. The horizontal transfer of antimicrobial resistance genes was thought to be due largely to conjugative plasmids or transposons, with only a minor part being played by transduction through bacteriophages. However, whole-genome sequencing has recently shown that the latter mechanism could be highly important in the exchange of antimicrobial resistance genes between microorganisms and environments. The transfer of antimicrobial resistance genes by phages could underlie the origin of resistant bacteria found in food. We show that chicken meat carries a number of phages capable of transferring antimicrobial resistance. Of 243 phages randomly isolated from chicken meat, about a quarter (24.7%) were able to transduce resistance to one or more of the five antimicrobials tested into Escherichia coli ATCC 13706 (DSM 12242). Resistance to kanamycin was transduced the most often, followed by that to chloramphenicol, with four phages transducing tetracycline resistance and three transducing ampicillin resistance. Phages able to transduce antimicrobial resistance were isolated from 44% of the samples of chicken meat that we tested. The statistically significant (P = 0.01) relationship between the presence of phages transducing kanamycin resistance and E. coli isolates resistant to this antibiotic suggests that transduction may be an important mechanism for transferring kanamycin resistance to E. coli. It appears that the transduction of resistance to certain antimicrobials, e.g., kanamycin, not only is widely distributed in E. coli isolates found on meat but also could represent a major mechanism for resistance transfer. The result is of high importance for animal and human health.

Characterization of Two Temperate Lactobacillus paracasei Bacteriophages: Morphology, Kinetics and Adsorption

Background/Aims: Adsorption and kinetic parameters, latent period, burst size and burst time, are characteristics of phage/host systems and can be affected by several environmental factors. As only few studies have focused on temperate dairy phages, we characterized these parameters on temperate Lactobacillus paracasei phages Φ iLp84 and Φ iLp1308, infective for probiotic strains. Methods: Phages were characterized by transmission electron microscopy and genomic DNA restriction. Adsorption under different environmental conditions, phage kinetics and efficiency of plating (EOP) were determined using the double-layer titration method. Results: Phages Φ iLp84 and Φ iLp1308 belong to the Siphoviridae family and have genome sizes of 38 and 34 kbp, respectively. Adsorption was affected by calcium concentration, pH, temperature and host viability, and reached a limit at very high multiplicity of infection. Latency, burst time and burst size were of 85 min, 131 min and 46 for Φ iLp84, and 51 min, 92 min and 28 for Φ iLp1308, respectively, at 37°C. A clear influence of temperature on phage kinetics was observed. Regarding EOP, Φ iLp84 produced plaques on only 1 out of 8 strains tested. Conclusion: Noticeable differences in adsorption, kinetics and EOP were found for two morphologically identical temperate L. paracasei phages of similar origin.

Bacteriophages and dairy fermentations

This review highlights the main strategies available to control phage infection during large-scale milk fermentation by lactic acid bacteria. The topics that are emphasized include the factors influencing bacterial activities, the sources of phage contamination, the methods available to detect and quantify phages, as well as practical solutions to limit phage dispersion through an adapted factory design, the control of air flow, the use of adequate sanitizers, the restricted used of recycled products, and the selection and growth of bacterial cultures.

Bacteriophages in food fermentations: new frontiers in a continuous arms race

Phage contamination represents an important risk to any process requiring bacterial growth, particularly in the biotechnology and food industries. The presence of unwanted phages may lead to manufacturing delays, lower quality product, or, in the worst cases, total production loss. Thus, constant phage monitoring and stringent application of the appropriate control measures are indispensable. In fact, a systematic preventive approach to phage contamination [phage analysis and critical control points (PACCP)] should be put in place. In this review, sources of phage contamination and novel phage detection methods are described, with an emphasis on bacterial viruses that infect lactic acid bacteria used in food fermentations. Recent discoveries related to antiphage systems that are changing our views on phage-host interactions are highlighted. Finally, future directions are also discussed.

Phages of lactic acid bacteria: the role of genetics in understanding phage-host interactions and their co-evolutionary processes

Dairy fermentations are among the oldest food processing applications, aimed at preservation and shelf-life extension through the use of lactic acid bacteria (LAB) starter cultures, in particular strains of Lactococcus lactis, Streptococcus thermophilus, Lactobacillus spp. and Leuconostoc spp. Traditionally this was performed by continuous passaging of undefined cultures from a finished fermentation to initiate the next fermentation. More recently, consumer demands on consistent and desired flavours and textures of dairy products have led to a more defined approach to such processes. Dairy (starter) companies have responded to the need to define the nature and complexity of the starter culture mixes, and dairy fermentations are now frequently based on defined starter cultures of low complexity, where each starter component imparts specific technological properties that are desirable to the product. Both mixed and defined starter culture approaches create the perfect environment for the proliferation of (bacterio)phages capable of infecting these LAB. The repeated use of the same starter cultures in a single plant, coupled to the drive towards higher and consistent production levels, increases the risk and negative impact of phage infection. In this review we will discuss recent advances in tracking the adaptation of phages to the dairy industry, the advances in understanding LAB phage-host interactions, including evolutionary and genomic aspects.

Review: efficiency of physical and chemical treatments on the inactivation of dairy bacteriophages

Bacteriophages can cause great economic losses due to fermentation failure in dairy plants. Hence, physical and chemical treatments of raw material and/or equipment are mandatory to maintain phage levels as low as possible. Regarding thermal treatments used to kill pathogenic bacteria or achieve longer shelf-life of dairy products, neither low temperature long time nor high temperature short time pasteurization were able to inactivate most lactic acid bacteria (LAB) phages. Even though most phages did not survive 90°C for 2 min, there were some that resisted 90°C for more than 15 min (conditions suggested by the International Dairy Federation, for complete phage destruction). Among biocides tested, ethanol showed variable effectiveness in phage inactivation, since only phages infecting dairy cocci and Lactobacillus helveticus were reasonably inactivated by this alcohol, whereas isopropanol was in all cases highly ineffective. In turn, peracetic acid has consistently proved to be very fast and efficient to inactivate dairy phages, whereas efficiency of sodium hypochlorite was variable, even among different phages infecting the same LAB species. Both alkaline chloride foam and ethoxylated non-ylphenol with phosphoric acid were remarkably efficient, trait probably related to their highly alkaline or acidic pH values in solution, respectively. Photocatalysis using UV light and TiO₂ has been recently reported as a feasible option to industrially inactivate phages infecting diverse LAB species. Processes involving high pressure were barely used for phage inactivation, but until now most studied phages revealed high resistance to these treatments. To conclude, and given the great phage diversity found on dairies, it is always advisable to combine different anti-phage treatments (biocides, heat, high pressure, photocatalysis), rather than using them separately at extreme conditions.