PHAGE: Therapy,Applications,and Research

The sustainability of Nile tilapia (Oreochromis niloticus) aquaculture is increasingly threatened by bacterial pathogens, such as Streptococcus agalactiae, which cause severe economic losses and high mortality. The overuse of antibiotics in aquaculture has worsened antimicrobial resistance, highlighting the need for alternative therapeutic strategies. This study examines the effectiveness of bacteriophage therapy under experimental conditions as a targeted, potentially environmentally friendly approach to control S. agalactiae infections in Nile tilapia by measuring survival, immune, biochemical, and histological endpoints.

Three lytic bacteriophages (STRA1, STRA2, STRA3) were isolated and characterized in vitro for host range and lytic activity against S. agalactiae. Experimental application used three administration methods: intramuscular injection of both bacteria and phage (Treat1), intramuscular bacterial infection followed by phage immersion (Treat2), and simultaneous immersion of fish in water containing both bacteria and phages (Treat3). Phage doses of 10⁵, 10⁷, and 10⁹ plaque-forming unit (PFU)/mL were tested. Outcomes evaluated included survival rates, immune responses, biochemical markers, histopathological recovery, and cytokine expression.

The results showed a dose-dependent decrease in mortality, with Treat1 achieving 100% relative percent survival at 10⁹ PFU/mL. Phage therapy significantly enhanced innate markers (nitroblue tetrazolium activity, lysozyme levels) and adaptive markers (total Ig, IgM), as well as glutathione S-transferase activity. Histological assessments revealed improved intestinal villus architecture, reduced kidney pathology, and enhanced tissue regeneration in groups treated with phages. Cytokine and gene expression analysis revealed a dose-dependent increase in interleukin (IL)-1β and IL-8 and in the antiviral MX gene, while TNF-α decreased at high doses. CXC2 (a chemokine) was also induced. Intramuscular administration consistently surpassed immersion methods, especially at intermediate doses, by providing more rapid and effective protection under the tested conditions.

This research highlights the potential of bacteriophage therapy as an alternative to antibiotics in aquaculture. The findings emphasize the importance of optimizing phage dosage and delivery techniques to enhance therapeutic effectiveness while reducing environmental impact. Future studies should focus on field validation, phage formulation strategies, and the long-term effects of phage therapy on fish health and microbiomes.

The escalating antibiotic resistance necessitates alternative strategies like bacteriophages, utilized in livestock for growth promotion and infectious disease treatment. To select promising phage candidates, this study aimed to characterize Escherichia phages with potential against swine-associated Escherichia coli.

Four E. coli phages were characterized for morphology, efficiency of plating, temperature stability, tolerance of simulated gastric fluid, long-term storage in various solutions, and lytic activity of individual and combined phages against pathogenic E. coli in tryptic soy broth and simulated intestinal fluid.

All phages exhibited infectivity and stability across 4°C–45°C, with varying sensitivity to low pH. The phages maintained stability in culture medium and select buffers at 4°C for at least 52 weeks. All phages exhibited significant lytic activity, with the cocktail showing enhanced reduction in certain conditions.

These four Escherichia phages demonstrate potential as biosanitation agents for swine housing and biocontrol strategies against swine colibacillosis, warranting further in vivo investigation.

Pseudomonas aeruginosa is an important etiological agent of diabetic foot ulcers. It is included in the World Health Organization’s priority list of organisms for which new antibiotics or alternatives are urgently needed. The rise in antimicrobial resistance highlights the urgent need to explore alternatives to antimicrobial drugs.

In this study, we isolated the bacteriophage Ps1.JH from hospital sewage water targeting a locally isolated strain of Pseudomonas aeruginosa.

Ps1.JH can inhibit bacterial growth for up to 24 h. It is stable at pH 4–9 and temperature up to 60°C. Ps1.JH has double stranded DNA genome of 72.67 kb with 55% GC content, encoding 91 open reading frames. According to ICTV classification, Ps1.JH belongs to the genus Litunavirus of Schitoviridae family. It does not encode any integrase, repressor, virulence factor, or toxin.

Ps1.JH could be a potential candidate for controlling P. aeruginosa of diabetic foot ulcer origin after further analyses.

Enterococcus faecium are gram-positive, multidrug-resistant bacteria that are endemic in healthcare settings. Bacteriophage therapy could be an adjunctive treatment for E. faecium infections.

We isolated four new Minhovirus phages using E. faecium strain ATCC 19434 as a host.

Phage genomes were each ∼19 kb in length, and were highly related to each other and to other previously isolated Minhovirus phages. Host range testing suggested a narrow spectrum of activity. In vitro-evolved phage-resistant mutants acquired mutations in the enterococcal polysaccharide antigen (epa) and capsular polysaccharide (cps) loci. Additional testing found that some phages were able to infect E. faecium clinical isolates with similar epa loci, further implicating epa as a putative receptor for Minhovirus phage infection.

Overall, this study increases our understanding of phages that target E. faecium and increases the number of characterized phages that are active against this important pathogen.

The majority of bacteriophages stop replicating once the host culture approaches the stationary phase. Only a few bacteriophages are able to replicate in host cells at the transition to, or already in, the early stationary phase of growth (early stationary phase infective, eSPI phages) have been characterized so far.

The coliphage DH23 was isolated from the river water using an enrichment procedure with a stationary phase culture of the host. Genomic sequencing, epigenetic modifications detection, and morphological and biological characterization were performed.

DH23 is a small siphovirus with a genome of 44,682 b.p. Phylogenetic analysis suggests that DH23 may be considered as a new species within the Dhillonvirus genus, closely related to Sodalis phage SO-1 and coliphage TheodorHerzl. Phage DH23 plaques continue to expand for several days of incubation and it is able to form plaques when applied to already mature 24 h-old host lawn.

Bacteriophage DH23 features an eSPI phenotype very similar to phage T7. Expanding the number of characterized eSPI coliphages may facilitate deciphering the molecular basis of eSPI phenotype and development of new eSPI platforms for phage therapy or other applications.