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

Evaluation of the in vitro and in vivo efficiency of in-feed bacteriophage cocktail application to control Salmonella Typhimurium and Salmonella Enteritidis infection in broiler chicks

RESEARCH HIGHLIGHTS

Bacteriophage (BP) cocktail was partially resistant to different temperatures and pH values.The BP cocktail showed lytic effects on different Salmonella isolates.The BP cocktail reduced Salmonella colonization in the internal organs of broilers.

Phenotypic characterization and genomic analysis of Limosilactobacillus fermentum phage

Limosilactobacillus (L.) fermentum is widely utilized for its beneficial properties, but lysogenic phages can integrate into its genome and can be induced to enter the lysis cycle under certain conditions, thus accomplishing lysis of host cells, resulting in severe economic losses. In this study, a lysogenic phage, LFP03, was induced from L. fermentum IMAU 32510 by UV irradiation for 70 s. The electron microscopy showed that this phage belonged to Caudoviricetes class. Its genome size was 39,556 bp with a GC content of 46.08%, which includes 20 functional proteins. Compared with other L. fermentum phages, the genome of phage LFP03 exhibited deletions, inversions and translocations. Biological analysis showed that its optimal multiplicity of infection was 0.1, with a burst size of 133.5 ± 4.9 PFU/infective cell. Phage LFP03 was sensitive to temperature and pH value, with a survival rate of 48.98% at 50 °C. It could be completely inactivated under pH 2. The adsorption ability of this phage was minimally affected by temperature and pH value, with adsorption rates reaching 80% under all treated conditions. Divalent cations could accelerate phage adsorption, while chloramphenicol expressed little influence. This study might expand the related knowledge of L. fermentum phages, and provide some theoretical basis for improving the stability of related products and establishing phage control measures.

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.

Characteristics and Whole-Genome Analysis of Limosilactobacillus fermentum Phage LFP02

Limosilactobacillus fermentum is a bacterium widely used in food production, medicine, and industrial fermentation. However, fermentation could fail due to phage contamination. L. fermentum bacteriophage LFP02 can be induced from L. fermentum IMAU 32579 using mitomycin C. To better understand the characteristics of this phage, its physiological and genomic characteristics were evaluated. The results showed that its optimal multiplicity of infection was 0.01, and the burst size was 148.03 ± 2.65 pfu/infective center. Compared to temperature, pH had a more obvious influence on phage viability, although its adsorption capacity was not affected by the divalent cations (Ca²⁺ and Mg²⁺) or chloramphenicol. Its genome size was 43,789 bp and the GC content was 46.06%, including 53 functional proteins. Compared to other L. fermentum phages, phage LFP02 had chromosome deletion, insertion, and inversion, which demonstrated that it was a novel phage. This study could expand the knowledge of the biological characteristics of L. fermentum bacteriophages and provide some theoretical basis for bacteriophage prevention during fermentation.

Exploring the Benefits of Metal Ions in Phage Cocktail for the Treatment of Methicillin-Resistant Staphylococcus aureus (MRSA) Infection

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is an important zoonotic pathogen worldwide. Infections due to MRSA are associated with higher mortality rates compared with methicillin-susceptible S. aureus. Meanwhile, bacteriophages have been shown to overcome the emergence of MRSA.

Methods

Phage PHB22a, PHB25a, PHB38a, and PHB40a were isolated. Here, we evaluated the ability of a phage cocktail containing phages PHB22a, PHB25a, PHB38a, and PHB40a against MRSA S-18 strain in vivo and in vitro. Phage whole-genome sequencing, host-range determination, lytic activity, and biofilm clearance experiments were performed in vitro. Galleria mellonella larvae and a mouse systemic infection model to evaluate the efficacy of phage therapy in vivo.

Results

The phage cocktail exhibited enhanced antibacterial and anti-biofilm effects compared to the single phage. Phage cocktail contained with Ca²⁺/Zn²⁺ significantly reduced the number of viable bacteria (24-h or 48-h biofilm) by more than 0.81-log compared to the phage cocktail alone. Furthermore, we demonstrated that the addition of Ca²⁺ and Zn²⁺ phage cocktail could increase the survival rate of G. mellonella larvae infected with S. aureus by 10% compared with phage cocktail alone. This was further confirmed in the mouse model, which showed a 2.64-log reduction of host bacteria S-18, when Ca²⁺ and Zn²⁺ were included in the cocktail compared with the phage cocktail alone.

Conclusion

Our results indicated that phage cocktail supplemented with Ca²⁺/Zn²⁺ could effectively remove bacteria in biofilms and mice tissues infected with S. aureus.

Isolation and Characterization of Novel Phages Targeting Xanthomonas oryzae: Culprit of Bacterial Leaf Blight Disease in Rice

Background: Bacterial leaf blight (BLB) disease caused 80% of disease incidence in paddy in Kedah and Selangor states of Malaysia. The pathogenic bacterium, Xanthomonas oryzae pv. oryzae (Xoo), is one of the destructive pathogens infecting lowland irrigated and rainfed paddy in Asia's tropical and temperate environments. Bacteriophages (or phages) have been proposed to control the pathogen due to their efficacy and safety aspects. Material and Methods: In this study, a total of 70 Xoo-phages were isolated from termite which living in rice-growing area. Results: 2 lytic phages NΦ-1 and NΦ-3 were selected due to the high titer of the virus. Electron microscopic analysis showed that those phages belonged to the family Podoviridae, order Caudovirales with short noncontracted tails. Moreover, these phages have a narrow host range specifically target Xoo with a higher burst size. Whole-genome sequencing showed that the Xoo-phage NΦ-1 and NΦ-3 consists of a linear double-stranded DNA molecule of length 41,151 and 38,454 bp, respectively. Conclusion: This study successfully characterized two novel Xanthomonas phages and their potential as antimicrobial agents against BLB disease in rice.

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.

The development of ghost vaccines trials

INTRODUCTION

Bacterial ghosts are intact bacterial cell envelopes that are emptied of their content by gentle biological or chemical poring methods. Ghost techniques increase the safety of the killed vaccines, while maintaining their antigenicity due to mild preparation procedures. Moreover, ghost-platforms may express and/or carry several antigens or plasmid-DNA encoding for protein epitopes.

AREAS COVERED

In this review, the development in ghost-vaccine production over the last 30 years is classified and discussed. The different applications of ghost-vaccines, how they trigger the immune system, their advantages and limitations are displayed. The phage-mediated lysis, molecular manipulation of the lysis-genes, and the biotechnological production of ghosts are described. The trials are classified according to the pattern of lysis and to the type of bacteria. Further subdivision includes chronological ordered application of the ghost as alternative-killed vaccine, recombinant antigen platform, plasmid DNA carrier, adjuvants, and dendritic cell inducer. Particular trials for specific pathogens or from distinct research schools are gathered.

EXPERT OPINION

Ghosts are highly qualified to act as immune-presenting platforms that express and/or carry several recombinant and DNA vaccines, as well as, being efficient alternative-killed vaccines. The coming years will show more molecular advances to develop ghost-production and to express more antigens.

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.

Characterization and adsorption of a Lactobacillus plantarum virulent phage

Bacteriophage infection of lactic acid bacteria is considered one of the biggest worldwide problems in the food industry. Bacteriophages may cause negative effects on the fermentation of various dairy-based products. A virulent bacteriophage was isolated from an abnormal fermentation liquid of Lactobacillus plantarum IMAU10120. The characterization and influence of temperature, pH, divalent cations, and chloramphenicol on the adsorption ability of this phage were evaluated. The results showed that this phage belonged to the Siphoviridae family. It exhibited a burst time of 135 min and a burst size of approximately 215 counts expressed per milliliter per infective center. No significant effect was shown to influence its viability and adsorption at 10 to 37°C. More than 90% of phages exhibited infectivity from pH 5 to 9. Divalent ions and chloramphenicol did not have a significant influence on the adsorption of this phage. The information obtained in this study will enrich the database of lactobacilli virulent phages and provide a basis of information for the control of phages in the food fermentation industry.

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.

Construction of Lactobacillus casei ghosts by Holin-mediated inactivation and the potential as a safe and effective vehicle for the delivery of DNA vaccines

BACKGROUND

Bacterial ghosts (BGs) are empty bacterial cell envelopes generated by releasing the cellular contents. In this study, a phage infecting Lactobacillus casei ATCC 393 (L. casei 393) was isolated and designated Lcb. We aimed at using L. casei 393 as an antigen delivery system to express phage-derived holin for development of BGs.

RESULTS

A gene fragment encoding holin of Lcb (hocb) was amplified by polymerase chain reaction (PCR). We used L. casei 393 as an antigen delivery system to construct the recombinant strain pPG-2-hocb/L. casei 393. Then the recombinants were induced to express hocb. The immunoreactive band corresponding to hocb was observed by western-blotting, demonstrating the efficiency and specificity of hocb expression in recombinants. The measurements of optical density at 600 nm (OD₆₀₀₎ after induction showed that expression of hocb can be used to convert L. casei cells into BGs. TEM showed that the cytomembrane and cell walls of hocb expressing cells were partially disrupted, accompanied by the loss of cellular contents, whereas control cells did not show any morphological changes. SEM showed that lysis pores were distributed in the middle or at the poles of the cells. To examine where the plasmid DNA was associated, we analyzed the L. casei ghosts loading SYBR Green I labeled pCI-EGFP by confocal microscopy. The result demonstrated that the DNA interacted with the inside rather than with the outside surface of the BGs. To further analyze where the DNA were loaded, we stained BGs with MitoTracker Green FM and the loaded plasmids were detected using EGFP-specific Cy-3-labeled probes. Z-scan sections through the BGs revealed that pCI-EGFP (red) was located within the BGs (green), but not on the outside. Flow cytometry and qPCR showed that the DNA was loaded onto BGs effectively and stably.

CONCLUSIONS

Our study constructed L. casei BGs by a novel method, which may be a promising technology for promoting the further application of DNA vaccine, providing experimental data to aid the development of other Gram-positive BGs.

Changes in Environmental Conditions Modify Infection Kinetics of Dairy Phages

Latent period, burst time, and burst size, kinetic parameters of phage infection characteristic of a given phage/host system, have been measured for a wide variety of lactic acid bacteria. However, most studies to date were conducted in optimal growth conditions of host bacteria and did not consider variations due to changes in external factors. In this work, we determined the effect of temperature, pH, and starvation on kinetic parameters of phages infecting Lactobacillus paracasei, Lactobacillus plantarum, and Leuconostoc mesenteroides. For kinetics assessment, one-step growth curves were carried out in MRS broth at optimal conditions (control), lower temperature, pH 6.0 and 5.0 (MRS₆ and MRS₅, respectively), or in medium lacking carbon (MRS_N) or nitrogen (MRS_C) sources. Phage infection was progressively impaired as environmental conditions were modified from optimal. At lower temperature or pH, infection was delayed, as perceived by longer latent and burst times. Burst size, however, was lower, equal or higher than for controls, but this effect was highly dependent on the particular phage-host system studied. Phage infection was strongly inhibited in MRS_C, but only mildly impaired in MRS_N. Nevertheless, growth of all the bacterial strains tested was severely compromised by starvation, without significant differences between MRS_C and MRS_N, indicating that nitrogen compounds are specifically required for a successful phage infection, beyond their influence on bacterial growth.

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.

The effect of bacteriophages on the acidification of a vegetable juice medium by microencapsulated Lactobacillus plantarum

Starter cultures are increasingly being used for the production of sauerkraut, kimchi and other fermented vegetables. The goal of this study was to determine whether the microencapsulation of a bacterial culture can prevent phage infection during vegetable fermentation. Lactobacillus plantarum HER1325 was microencapsulated in alginate beads. Some beads were used without further processing, while others were freeze-dried prior to testing. Fresh beads (diameter of 2 mm) and dried cultures of the lactobacilli (particle size of 53-1000 μm) were added to a vegetable juice medium (VJM) at 1 × 10⁷ CFU/mL. The virulent phage HER325 was added at an initial titer of 1 × 10⁴ PFU/mL. In the absence of phages, the pH of the vegetable juice dropped to 4.2 after 40 h of fermentation at 19 °C. In the presence of phage HER325, acidification by both the non-microencapsulated and microencapsulated starter cultures stopped after 24 h. In all assays, the alginate particles dissolved during the 40 h of VJM fermentation. When 15 g/L of calcium chloride was added to the VJM, the alginate beads did not dissolve and significant phage protection was observed. The results suggest that phage-protected microencapsulated starter cultures can be used for vegetable fermentation if means are taken to prevent them from dissolving during acidification.