Thermal and chemical resistance of Lactobacillus casei and Lactobacillus paracasei bacteriophages

Bacteriophage Challenges in Industrial Processes: A Historical Unveiling and Future Outlook

Humans have used fermentation processes since the Neolithic period, mainly to produce beverages. The turning point occurred in the 1850s, when Louis Pasteur discovered that fermentation resulted from the metabolism of living microorganisms. This discovery led to the fast development of fermented food production. The importance of industrial processes based on fermentation significantly increased. Many branches of industry rely on the metabolisms of bacteria, for example, the dairy industry (cheese, milk, yogurts), pharmaceutical processes (insulin, vaccines, antibiotics), or the production of chemicals (acetone, butanol, acetic acid). These are the mass production processes involving a large financial outlay. That is why it is essential to minimize threats to production. One major threat affecting bacteria-based processes is bacteriophage infections, causing substantial economic losses. The first reported phage infections appeared in the 1930s, and companies still struggle to fight against phages. This review shows the cases of phage infections in industry and the most common methods used to prevent phage infections.

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.

Characterization and genomic analysis of a novel lytic phage vB_PstM_ZRG1 infecting Stutzerimonas stutzeri, representing a new viral genus, Elithevirus

Stutzerimonas stutzeri is an opportunistic pathogen widely distributed in the environment and displays diverse metabolic capabilities. In this study, a novel lytic S. stutzeri phage, named vB_PstM_ZRG1, was isolated from the seawater in the East China Sea (29°09'N, 123°39'E). vB_PstM_ZRG1 was stable at temperatures ranging from -20°C to 65°C and across a wide range of pH values from 3 to 10. The genome of vB_PstM_ZRG1 was determined to be a double-stranded DNA with a genome size of 52,767 bp, containing 78 putative open reading frames (ORFs). Three auxiliary metabolic genes encoded by phage vB_PstM_ZRG1 were predicted, including Toll/interleukin-1 receptor (TIR) domain, proline-alanine-alanine-arginine (PAAR) protein and SGNH (Ser-Gly-Asn-His) family hydrolase, especially TIR domain is not common in isolated phages. Phylogenic and network analysis showed that vB_PstM_ZRG1 has low similarity to other phage genomes in the GenBank and IMG/VR database, and might represent a novel viral genus, named Elithevirus. Additionally, the distribution map results indicated that vB_PstM_ZRG1 could infect both extreme colds- and warm-type hosts in the marine environment. In summary, our finding provided basic information for further research on the relationship between S. stutzeri and their phages, and expanded our understanding of genomic characteristics, phylogenetic diversity and distribution of Elithevirus.

Isolation and characterization of a novel mycobacteriophage Kashi-VT1 infecting Mycobacterium species

Mycobacteriophages are viruses that infect members of genus Mycobacterium. Because of the rise in antibiotic resistance in mycobacterial diseases such as tuberculosis, mycobacteriophages have received renewed attention as alternative therapeutic agents. Mycobacteriophages are highly diverse, and, on the basis of their genome sequences, they are grouped into 30 clusters and 10 singletons. In this article, we have described the isolation and characterization of a novel mycobacteriophage Kashi-VT1 (KVT1) infecting Mycobacterium >smegmatis mc2 155 (M. smegmatis) and Mycobacterium fortuitum isolated from Varanasi, India. KVT1 is a cluster K1 temperate phage that belongs to Siphoviridae family as visualized in transmission electron microscopy. The phage genome is 61,010 base pairs with 66.5% Guanine/Cytosine (GC) content, encoding 101 putative open reading frames. The KVT1 genome encodes an immunity repressor, a tyrosine integrase, and an excise protein, which are the characteristics of temperate phages. It also contains genes encoding holin, lysin A, and lysin B involved in host cell lysis. The one-step growth curve demonstrated that KVT1 has a latency time of 90 min and an average burst size of 101 phage particles per infected cell. It can withstand a temperature of up to 45°C and has a maximum viability between pH 8 and 9. Some mycobacteriophages from cluster K are known to infect the pathogenic Mycobacterium tuberculosis (M. tuberculosis); hence, KVT1 holds potential for the phage therapy against tuberculosis, and it can also be engineered to convert into an exclusively lytic phage.

The incorporation of peach gum polysaccharide into soy protein based microparticles improves probiotic bacterial survival during simulated gastrointestinal digestion and storage

The objective of this research was to investigate the in vitro gastrointestinal digestion and storage properties of Lactobacillus plantarum 550 encapsulated in soy protein isolate (SPI) and peach gum polysaccharide (PG) through spray drying. High survival rates (>8.1 Log CFU/g) were obtained for all encapsulation formulas containing PG. Combination of SPI and PG showed positive effects on both gastric resistance and storage stability of cells. Among the formulas tested, sample of SPI:PG = 3:1 showed the highest survival (7.88 ± 0.12 Log CFU/g), corresponding to the strongest electrostatic interaction between SPI and PG. With PG content increasing, the storage stability of probiotic was also enhanced, as PG could reduce the moisture content within microcapsules as well as scavenge free radicals generated during storage. In conclusion, the current study demonstrates that SPI combined with PG may provide effective protection to cells not only during spray drying, but also during storage and gastrointestinal digestion.

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.

Isolation, Characterization, and Genomic Analysis of Three Novel E. coli Bacteriophages That Effectively Infect E. coli O18

Escherichia coli (E. coli) is one of the most common pathogenic bacteria worldwide. Avian pathogenic E. coli (APEC) causes severe systemic disease in poultry (Colibacillosis), and accordingly, has an extreme risk to the poultry industry and public health worldwide. Due to the increased rate of multi-drug resistance among these bacteria, it is necessary to find an alternative therapy to antibiotics to treat such infections. Bacteriophages are considered one of the best solutions. This study aimed to isolate, characterize, and evaluate the potential use of isolated bacteriophages to control E. coli infections in poultry. Three novel phages against E. coli O18 were isolated from sewage water and characterized in vitro. The genome size of the three phages was estimated to be 44,776 bp, and the electron microscopic analysis showed that they belonged to the Siphoviridae family, in the order Caudovirales. Phages showed good tolerance to a broad range of pH and temperature. The complete genomes of three phages were sequenced and deposited into the GenBank database. The closely related published genomes of Escherichia phages were identified using BLASTn alignment and phylogenetic trees. The prediction of the open reading frames (ORFs) identified protein-coding genes that are responsible for functions that have been assigned such as cell lysis proteins, DNA packaging proteins, structural proteins, and DNA replication/transcription/repair proteins.

Topically Applied Bacteriophage to Control Multi-Drug Resistant Klebsiella pneumoniae Infected Wound in a Rat Model

(Background): Multi-drug-resistant Klebsiella pneumoniae (MDR-KP) has steadily grown beyond antibiotic control. Wound infection kills many patients each year, due to the entry of multi-drug resistant (MDR) bacterial pathogens into the skin gaps. However, a bacteriophage (phage) is considered to be a potential antibiotic alternative for treating bacterial infections. This research aims at isolating and characterizing a specific phage and evaluate its topical activity against MDR-KP isolated from infected wounds. (Methods): A lytic phage ZCKP8 was isolated by using a clinical isolate KP/15 as a host strain then characterized. Additionally, phage was assessed for its in vitro host range, temperature, ultraviolet (UV), and pH sensitivity. The therapeutic efficiency of phage suspension and a phage-impeded gel vehicle were assessed in vivo against a K. pneumoniae infected wound on a rat model. (Result): The phage produced a clear plaque and was classified as Siphoviridae. The phage inhibited KP/15 growth in vitro in a dose-dependent pattern and it was found to resist high temperature (˂70 °C) and was primarily active at pH 5; moreover, it showed UV stability for 45 min. Phage-treated K. pneumoniae inoculated wounds showed the highest healing efficiency by lowering the infection. The quality of the regenerated skin was evidenced via histological examination compared to the untreated control group. (Conclusions): This research represents the evidence of effective phage therapy against MDR-KP.

Bacteriophage treatment before chemical disinfection can enhance removal of plastic surface-associated Pseudomonas aeruginosa

Opportunistic pathogens can linger on surfaces in hospital and building plumbing environments, leading to infections in at-risk populations. Further, biofilm-associated bacteria are protected from removal and inactivation protocols, such as disinfection. Bacteriophages show promise as tools to treat antibiotic resistant infections. As such, phages may also be useful in environmental applications to prevent newly acquired infections. In the current study, the potential of synergies between bacteriophage and chemical disinfection of the opportunistic pathogen Pseudomonas aeruginosa was assessed under various conditions. Specifically, surface-associated P. aeruginosa was treated with various concentrations of phages (P1 or JG004), chemical disinfectant (sodium hypochlorite or benzalkonium chloride), or combined sequential treatments under three distinct attachment models (spot inoculations, dry biofilms, and wet biofilms). Phages were very effective at removing bacteria in spot inoculation (>3.2 log₁₀ removal) and wet biofilms (up to 2.6 log₁₀ removal), while phages prevented regrowth of dry biofilms in the application time. In addition, phage treatment followed by chemical disinfection inactivated more P. aeruginosa under wet biofilm conditions better than either treatment alone. This effect was hindered when chemical disinfection was applied first, followed by phage treatment, suggesting additive benefits of combination treatments are lost when phage is applied last. Further, we confirm prior evidence of greater phage tolerance to benzalkonium chloride relative to sodium hypochlorite, informing choices for combination phage-disinfectant approaches. Overall, this paper further supports the potential of using combination phage and chemical disinfectant treatments to improve inactivation of surface-associated P. aeruginosa. Importance Phages are already utilized in the healthcare industry to treat antibiotic resistant infections, such as on implant-associated biofilms and in compassionate care cases. Phage treatment could also be a promising new tool to control pathogens in the built environment, preventing infections from occurring. This study shows that phage can be combined effectively with chemical disinfectants to improve removal of wet biofilms and bacteria spotted onto surfaces while preventing regrowth in dry biofilms. This has the potential to improve pathogen containment within the built environment and drinking water infrastructure to prevent infections of opportunistic pathogens.

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.

Lysin LysMK34 of Acinetobacter baumannii Bacteriophage PMK34 Has a Turgor Pressure-Dependent Intrinsic Antibacterial Activity and Reverts Colistin Resistance

The prevalence of extensively and pandrug-resistant strains of Acinetobacter baumannii leaves little or no therapeutic options for treatment for this bacterial pathogen. Bacteriophages and their lysins represent attractive alternative antibacterial strategies in this regard. We used the extensively drug-resistant A. baumannii strain MK34 to isolate the bacteriophage PMK34 (vB_AbaP_PMK34). This phage shows fast adsorption and lacks virulence genes; nonetheless, its narrow host spectrum based on capsule recognition limits broad application. PMK34 is a Fri1virus member of the Autographiviridae and has a 41.8-kb genome (50 open reading frames), encoding an endolysin (LysMK34) with potent muralytic activity (1,499.9 ± 131 U/μM), a typical mesophilic thermal stability up to 55°C, and a broad pH activity range (4 to 10). LysMK34 has an intrinsic antibacterial activity up to 4.8 and 2.4 log units for A. baumannii and Pseudomonas aeruginosa strains, respectively, but only when a high turgor pressure is present. The addition of 0.5 mM EDTA or application of an osmotic shock after treatment can compensate for the lack of a high turgor pressure. The combination of LysMK34 and colistin results in up to 32-fold reduction of the MIC of colistin, and colistin-resistant strains are resensitized in both Mueller-Hinton broth and 50% human serum. As such, LysMK34 may be used to safeguard the applicability of colistin as a last-resort antibiotic.IMPORTANCE A. baumannii is one of the most challenging pathogens for which development of new and effective antimicrobials is urgently needed. Colistin is a last-resort antibiotic, and even colistin-resistant A. baumannii strains exist. Here, we present a lysin that sensitizes A. baumannii for colistin and can revert colistin resistance to colistin susceptibility. The lysin also shows a strong, turgor pressure-dependent intrinsic antibacterial activity, providing new insights in the mode of action of lysins with intrinsic activity against Gram-negative bacteria.

Characterization and Genome Analysis of a Novel Marine Alteromonas Phage P24

Although Alteromonas is ubiquitous in the marine environment, very little is known about Alteromonas phages, with only ten, thus far, being isolated and reported on. In this study, a novel double-stranded DNA phage, Alteromonas phage P24, which infects Alteromonas macleodii, was isolated from the coastal waters off Qingdao. Alteromonas phage P24 has a siphoviral morphology, with an icosahedral head, 61 ± 1 nm in diameter, and a tail length of 105 ± 1 nm. Alteromonas phage P24 contains lipids. It has an optimal temperature and pH for growth of 20℃ and 5-7, respectively. A one-step growth curve shows a latent period of 55 min, a rise period of 65 min, and an average burst size of approximately 147 virions per cell. Alteromonas phage P24 has the genome of 46,945 bp with 43.80% GC content and 74 open reading frames (ORFs) without tRNA. The results of the phylogenetic tree, based on the mcp and terL genes, show that Alteromonas phage P24 is closely related to Aeromonas phage phiARM81ld. Meanwhile, phylogenetic analysis based on the whole genome of P24 indicates that it forms a unique viral sub-cluster within Siphoviridae. This study contributes to the understanding of the genomic characteristics and the virus-host interactions of Alteromonas phages.

Acid tolerance and morphological characteristics of five Weissella cibaria bacteriophages isolated from kimchi

Five bacteriophages were isolated from kimchi with the hosts of two Weissella cibaria and acid-producing bacteria, and characterized for understanding Weissella phage. By transmission electron microscope, фWC51 and фWC52 belonged to the Myoviridae and фWC005, фWC130, and фWC248 belonged to the Podoviridae. One-step growth curves showed that latent periods of bacteriophages ranged from 70 to 90 min and burst sizes ranged from 7 to 195 particles/cell. фWC51 and фWC005 were thermally resistant than the others and those D values were 71 and 34 s at 70 °C. pH stability test at pH 2.0-4.0 showed фWC005 was most stable and the others were also stable at low pH of 3.0. Interestingly, the phages showed two types of morphology and had a high tolerance under acidic condition, therefore, which might cause mortality to the Weissella after middle stage of kimchi fermentation.

Polyvalent Phage CoNShP-3 as a Natural Antimicrobial Agent Showing Lytic and Antibiofilm Activities against Antibiotic-Resistant Coagulase-Negative Staphylococci Strains

Synthetic antimicrobials have a negative impact on food quality and consumer health, which is why natural antimicrobials are urgently needed. Coagulase-negative staphylococci (CoNS) has gained considerable importance for food poisoning and infection in humans and animals, particularly in biofilms. As a result, this study was conducted to control the CoNS isolated from food samples in Egypt. CoNS isolates were selected on the basis of their antibiotic susceptibility profiles and their biofilm-associated behavior. In this context, a total of 29 different bacteriophages were isolated and, in particular, lytic phages (6 isolates) were selected. The host range and physiological parameters of the lytic phages have been studied. Electron microscopy images showed that lytic phages were members of the families Myoviridae (CoNShP-1, CoNShP-3, and CoNSeP-2 isolates) and Siphoviridae (CoNShP-2, CoNSsP-1, and CoNSeP-1 isolates). CoNShP-1, CoNShP-2, and CoNShP-3 were found to be virulent to Staphylococcus haemolyticus, CoNSsP-1 to Staphylococcus saprophyticus and CoNSeP-1 and CoNSeP-2 to Staphylococcus epidermidis. Interestingly, the CoNShP-exhibited a typical polyvalent behavior, where not only lysis CoNS, but also other genera include Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Staphylococcus aureus (VRSA), Bacillus cereus and Bacillus subtilis. In addition, CoNShP-3 phage showed high stability at different temperatures and pH levels. Indeed, CoNShP-3 phage showed an antibiofilm effect against Staphylococcus epidermidis CFS79 and Staphylococcus haemolyticus CFS43, respectively, while Staphylococcus saprophyticus CFS28 biofilm was completely removed. Finally, CoNShP-3 phage demonstrated a high preservative efficacy over short and long periods of storage against inoculated CoNS in chicken breast sections. In conclusion, this study highlights the control of CoNS pathogens using a polyvalent lytic phage as a natural antibacterial and antibiofilm agent from a food safety perspective.

Isolation and Genome Sequencing of a Novel Pseudomonas aeruginosa Phage PA-YS35

Phage PA-YS35 is a novel lytic Pseudomonas aeruginosa phage belonging to the Myoviridae family and was isolated from the sewage of the First Hospital of Jilin University. The biological properties testing indicated that phage PA-YS35 is stable between - 20 and 60 °C and pH 4-9. The one-step growth curve shows that the latent period of PA-YS35 was 9 min, and the burst period was about 21 min by the size of approximately 380 progeny phages per host cell. The genome of phage PA-YS35 is linear double-stranded DNA with a size of 93,296 bp and a GC content of 49.35%. The results from RAST gene annotation analysis showed that the PA-YS35 genome contains 172 open reading frames (ORFs); the function of 41 ORFs can be predicted, whereas the product of remaining 131 ORFs are hypothetical proteins. According to phylogenetic tree of RNA ligase encoding sequence, phage PA-YS35 has a close evolutionary relationship with Pseudomonas phage PAK P1 because both of them are located on the same branch. The study of phage PA-YS35 genome will provide useful information for further research on the interaction between phages and their hosts.

Complete genomic sequence of bacteriophage P23: a novel Vibrio phage isolated from the Yellow Sea, China

A novel Vibrio phage, P23, belonging to the family Siphoviridae was isolated from the surface water of the Yellow Sea, China. The complete genome of this phage was determined. A one-step growth curve showed that the latent period was approximately 30 min, the burst size was 24 PFU/cell, and the rise period was 20 min. The phage is host specific and is stable over a range of pH (5-10) and temperatures (4-65 °C). Transmission electron microscopy showed that phage P23 can be categorized into the Siphoviridae family, with an icosahedral head of 60 nm and a long noncontractile tail of 144 nm. The genome consisted of a linear, double-stranded 40.063 kb DNA molecule with 42.5% G+C content and 72 putative open reading frames (ORFs) without tRNA. The predicted ORFs were classified into six functional groups, including DNA replication, regulation and nucleotide metabolism, transcription, phage packaging, phage structure, lysis, and hypothetical proteins. The Vibrio phage P23 genome is a new marine Siphoviridae-family phage genome that provides basic information for further molecular research on interaction mechanisms between bacteriophages and their hosts.

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.

A Novel Phage PD-6A3, and Its Endolysin Ply6A3, With Extended Lytic Activity Against Acinetobacter baumannii

With widespread abuse of antibiotics, bacterial resistance has increasingly become a serious threat. Acinetobacter baumannii has emerged as one of the most important hospital-acquired pathogens worldwide. Bacteriophages (also called “phages”) could be used as a potential alternative therapy to meet the challenges posed by such pathogens. Endolysins from phages have also been attracting increasing interest as potential antimicrobial agents. Here, we isolated 14 phages against A. baumannii, determined the lytic spectrum of each phage, and selected one with a relatively broad host range, named vB_AbaP_PD-6A3 (PD-6A3 for short), for its biological characteristics. We over-expressed and purified the endolysin (Ply6A3) from this phage and tested its biological characteristics. The PD-6A3 is a novel phage, which can kill 32.4% (179/552) of clinical multidrug resistant A. baumannii (MDRAB) isolates. Interestingly, in vitro, this endolysin could not only inhibit A. baumannii, but also that of other strains, such as Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA). We found that lethal A. baumannii sepsis mice could be effectively rescued in vivo by phage PD-6A3 and endolysin Ply6A3 intraperitoneal injection. These characteristics reveal the promising potential of phage PD-6A3 and endolysin Ply6A3 as attractive candidates for the control of A. baumannii-associated nosocomial infections.

Complete genome analysis of a Siphoviridae phage TSK1 showing biofilm removal potential against Klebsiella pneumoniae

Multidrug-resistant Klebsiella pneumoniae is a nosocomial pathogen, produces septicemia, pneumonia and UTI. Excessive use of antibiotics contributes towards emergence of multidrug-resistance. Bacteriophage-therapy is a potential substitute of antibiotics with many advantages. In this investigation, microbiological and genome characterization of TSK1 bacteriophage and its biofilm elimination capability are presented. TSK1 showed narrow host range and highest stability at pH 7 and 37 °C. TSK1 reduced the growth of K. pneumoniae during the initial 14 hours of infection. Post-treatment with TSK1 against different age K. pneumoniae biofilms reduced 85-100% biomass. Pre-treatment of TSK1 bacteriophage against the biofilm of Klebsiella pneumoniae reduced > 99% biomass in initial 24 hr of incubation. The genome of TSK1 phage comprised 49,836 base pairs with GC composition of 50.44%. Total seventy-five open reading frames (ORFs) were predicted, 25 showed homology with known functional proteins, while 50 were called hypothetical, as no homologs with proved function exists in the genome databases. Blast and phylogenetic analysis put it in the Kp36 virus genus of family Siphoviridae. Proposed packaging strategy of TSK1 bacteriophage genome is headful packaging using the pac sites. The potential of TSK1 bacteriophage could be used to reduce the bacterial load and biofilm in clinical and non-clinical settings.

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.

Isolation and Complete Genome Sequence of a Novel Marinobacter Phage B23

We used the double-agar layer method to isolate a novel Marinobacter marina bacteriophage, B23, from the surface water sample of the Bohai sea of China. There is some work to better understand the phage. The result of transmission electron microscopy revealed that B23 belongs to the family Siphoviridae with a head of 80 nm in diameter and a tail of 230 nm. Microbiological characterization evidenced that phage B23 is stable at the temperatures from - 25 to 60 °C, and showed vigorous vitality at pH between 4.0 and 12.0. One-step growth experiment showed that it had a longer latent period and higher lysis efficiency. Furthermore, the complete genome of B23 was sequenced and analyzed, which consists of a 35132 bp DNA with a G + C content of 59.8% and 50 putative open reading frames. The genome was divided into five parts, consisting of DNA replication and regulation, phage packaging, phage structure, host lysis and hypothetical protein.

Bacteriophage ZCKP1: A Potential Treatment for Klebsiella pneumoniae Isolated From Diabetic Foot Patients

The recorded growth in infection by multidrug resistant bacteria necessitates prompt efforts toward developing alternatives to antibiotics, such as bacteriophage therapy. Immuno-compromised patients with diabetes mellitus are particularly prone to foot infections by multidrug resistant Klebsiella pneumoniae, which may be compounded by chronic osteomyelitis. Bacteriophage ZCKP1, isolated from freshwater in Giza, Egypt, was tested in vitro to evaluate its lytic activity against a multidrug resistant K. pneumoniae KP/01, isolated from foot wound of a diabetic patient in Egypt. Characterization of ZCKP1 phage indicated that it belonged to the Myoviridae family of bacteriophages with a ds-DNA genome size of 150.9 kb. Bacteriophage ZCKP1 lysed a range of osteomyelitis pathogenic agents including Klebsiella spp., Proteus spp. and E. coli isolates. The bacteriophage reduced the bacterial counts of host bacteria by ≥2 log₁₀ CFU/ml at 25°C, and demonstrated the ability to reduce bacterial counts and biofilm biomass (>50%) when applied at high multiplicity of infection (50 PFU/CFU). These characteristics make ZCKP1 phage of potential therapeutic value to treat K. pneumoniae and associated bacteria present in diabetic foot patients.

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.

Characterization of Bacteriophages Infecting Clinical Isolates of Clostridium difficile

Clostridium difficile is recognized as a problematic pathogen, causing severe enteric diseases including antibiotic-associated diarrhea and pseudomembranous colitis. The emergence of antibiotic resistant C. difficile has driven a search for alternative anti-infection modalities. A promising strategy for controlling bacterial infection includes the use of bacteriophages and their gene products. Currently, knowledge of phages active against C. difficile is still relatively limited by the fact that the isolation of phages for this organism is a technically demanding method since bacterial host themselves are difficult to culture. To isolate and characterize phages specific to C. difficile, a genotoxic agent, mitomycin C, was used to induce temperate phages from 12 clinical isolates of C. difficile. Five temperate phages consisting of ΦHR24, ΦHN10, ΦHN16-1, ΦHN16-2, and ΦHN50 were successfully induced and isolated. Spotting assays were performed against a panel of 92 C. difficile isolates to screen for susceptible bacterial hosts. The results revealed that all the C. difficile phages obtained in this work displayed a relatively narrow host range of 0-6.5% of the tested isolates. Electron microscopic characterization revealed that all isolated phages contained an icosahedral head connected to a long contractile tail, suggesting that they belonged to the Myoviridae family. Restriction enzyme analysis indicated that these phages possess unique double-stranded DNA genome. Further electron microscopic characterization revealed that the ΦHN10 absorbed to the bacterial surface via attachment to cell wall, potentially interacting with S-layer protein. Bacteriophages isolated from this study could lead to development of novel therapeutic agents and detection strategies for C. difficile.

Isolation and Characterization of a Phage to Control Vancomycin Resistant Enterococcus Faecium

Enterococcus faecium, is an important nosocomial pathogen with increased incidence of multidrug resistance (MDR) - specifically Vancomycin resistance. E. faecium constitutes the normal microbiota of the human intestine as well as exists in the hospitals and sewage, thus making the microorganism difficult to eliminate. Phage therapy has gained attention for controlling bacterial MDR infections and contaminations. We have successfully isolated from waste water and characterized a lytic bacteriophage STH1 capable of targeting Vancomycin resistant Enterococcus faecium (VREF) with high specificity. The phage was isolated from sewage water of a hospital at district Dera Ismail Khan, Pakistan. Initial characterization showed that magnesium and calcium ions significantly increased phage adsorption to the host. One step growth experiment showed a latent period of 18 min with burst size of 334 virions per cell. Optimal temperature and pH of the phage was 37°C and 7.0, respectively. Phage application to host strain grown in milk and water (treated and untreated) showed that the phage efficiently controlled bacterial growth. The study suggests that the phage STH1 can serve as potential control agent for E. faecium infections in medical facilities and in other environmental contaminations.

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.

Effectiveness of a Lytic Phage SRG1 against Vancomycin-Resistant Enterococcus faecalis in Compost and Soil

Nosocomial infections caused by vancomycin-resistant Enterococcus have become a major problem. Bacteriophage therapy is proposed as a potential alternative therapy. Bacteriophages are viruses that infect bacteria and are ubiquitous in nature. Lytic bacteriophage was isolated from sewage water that infects VREF, the causative agent of endocarditis, bacteraemia, and urinary tract infections (UTIs). The phage produced clear plaques with unique clear morphology and well-defined boundaries. TEM results of phage revealed it to be 108 ± 0.2 nm long and 90 ± 0.5 nm wide. The characterization of bacteriophage revealed that infection process of phage was calcium and magnesium dependent and phage titers were highest under optimum conditions for VREF, with an optimal temperature range of 37–50°C. The maximum growth was observed at 37°C, hence having 100% viability. The latent period for phage was small with a burst size of 512 viral particles per bacterial cell. The phage was tested against various clinical strains and results proved it to be host specific. It can be used as a potential therapeutic agent for VREF infections. The phage efficiently eradicated VREF inoculated in cattle compost, poultry compost, and a soil sample which makes it a potential agent for clearing compost and soil sample.

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.

Isolation and Genome Sequencing of a Novel Pseudoalteromonas Phage PH1

The family Pseudoalteromonas is highly adaptable to dissimilar ecological habitats and plays an important ecological role in the marine environment. In this study, a new Pseudoalteromonas phage PH1 was isolated from the Yellow Sea. To better understand the bacteriophage, its biological properties, including morphology, host range, growth phenotype, thermal and pH stability, and nucleic acid composition, were investigated in detail. The result showed that the phage PH1 is a Podoviridae-phage with an icosahedral head (60 nm of diameter) and a short tail (26 nm in length). The phage PH1 genome consists of 42,685 bp length double-stranded DNA with a G+C content of 42.24% and is predicted to have 55 open reading frames (ORFs) with an average length of 740 bp nucleotides each. The phage PH1 genome adds a new Podoviridae-phage genome to marine bacteriophage dataset, which will provide useful basic information for further molecular research on interaction mechanisms between bacteriophages and their hosts.

Experimental Phage Therapy for Burkholderia pseudomallei Infection

Burkholderia pseudomallei is an intracellular Gram-negative bacterial pathogen intrinsically resistant to a variety of antibiotics. Phages have been developed for use as an alternative treatment therapy, particularly for bacterial infections that do not respond to conventional antibiotics. In this study, we investigated the use of phages to treat cells infected with B. pseudomallei. Phage C34 isolated from seawater was purified and characterised on the basis of its host range and morphology using transmission electron microscopy (TEM). Phage C34 was able to lyse 39.5% of B. pseudomallei clinical strains. Due to the presence of contractile tail, phage C34 is classified as a member of the family Myoviridae, a tailed double-stranded DNA virus. When 2 × 10⁵ A549 cells were exposed to 2 × 10⁷ PFU of phage C34, 24 hours prior to infection with 2 × 10⁶ CFU of B. pseudomallei, it was found that the survivability of the cells increased to 41.6 ± 6.8% as compared to 22.8 ± 6.0% in untreated control. Additionally, application of phage successfully rescued 33.3% of mice infected with B. pseudomallei and significantly reduced the bacterial load in the spleen of the phage-treated mice. These findings indicate that phage can be a potential antimicrobial agent for B. pseudomallei infections.

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.

Isolation and Characterization of a Novel Virulent Phage of Lactobacillus casei ATCC 393

A new virulent phage (Lcb) of Lactobacillus casei ATCC 393 was isolated from Chinese sauerkraut. It was specific to L. casei ATCC 393. Electron micrograph revealed that it had an icosahedral head (60.2 ± 0.8 nm in diameter) and a long tail (251 ± 2.6 nm). It belonged to the Siphoviridae family. The genome of phage Lcb was estimated to be approximately 40 kb and did not contain cohesive ends. One-step growth kinetics of its lytic development revealed latent and burst periods of 75 and 45 min, respectively, with a burst size of 16 PFU per infected cell. The phage was able to survive in a pH range between 4 and 11. However, a treatment of 70 °C for 30 min and 75% ethanol or isopropanol for 20 min was observed to inactivate phage Lcb thoroughly. The presence of both Ca(2+) and Mg(2+) showed a little influence on phage adsorption, but they were indispensable to gain complete lysis and improve plaque formation. The adsorption kinetics were similar on viable or nonviable cells, and high adsorption rates maintained between 10 and 37 °C. The highest adsorption rate was at 30 °C. This study increased the knowledge on phages of L. casei. The characterization of phage Lcb is helpful to establish a basis for adopting effective strategies to control phage attack in industry.

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.

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.