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ARS Home » Southeast Area » Auburn, Alabama » Aquatic Animal Health Research » Research » Research Project #442692

Research Project: Phage Endolysins as Alternatives to Antibiotics for Treating Systemic Infections of Streptococcus Iniae in Fish

Location: Aquatic Animal Health Research

Project Number: 6010-32000-027-033-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Jun 1, 2022
End Date: Apr 15, 2024

1. Demonstrate efficacy of the optimal constructs (high activity and high species-specificity peptidoglycan hydrolases (PGH’s) and PGH fused to protein transduction domains (PGH-PTDs) to therapeutically treat Streptococcus iniae in an established Nile tilapia (Oreochromis niloticus) disease model. The work will explore the possibility of using these enzymes as alternatives to antibiotics for treating this major pathogen of tilapia using both injection delivery and as a feed through additive. 2. Training of University of Arkansas Pine Bluff (UAPB) and Virginia State University (VSU) students in the infectious disease models using fish as experimental animals to build the schools' capacity.

Streptococcus iniae, a Gram positive bacteria, is recognized as an emerging or re-emerging pathogen of wild and cultured fish with ~30 species susceptible. The worldwide economic impact of streptococcosis to the global aquaculture industry is billions of dollars annually. S. iniae is a significant deterrent to the successful farming of aquaculture species. Although antibiotic treatment may be effective, the use of antibiotics in animal production has recently fallen under scrutiny with the development of multi-drug resistant strains and the potential for farm-to-clinic antibiotic-resistance transfer. There is a need for alternative (non-antibiotic) antimicrobials that are refractory to resistance development. We hypothesize that phage endolysins [cell wall degrading peptidoglycan hydrolases (PGHs)] are enzyme antimicrobials that can prevent and/or eradicate both planktonic and intracellular S. iniae from fish as either a systemic or topical infection. PGHs digest peptidoglycan, the major structural component of Gram positive bacterial cell walls. This seed grant is between three 1890 Historically Black Colleges or University (HBCU) and two Agriculture Research Service (ARS), USDA locations with interest in fish diseases: University of Arkansas Pine Bluff, (UAPB; an 1890 HBCU), Kentucky State University (KSU; an 1890 HBCU), Virginia State University (VSU; an 1890 HBCU) and ARS, USDA (Peoria, Ill and Auburn, AL). This proposal will characterize two PGH antimicrobials known to kill S. iniae and demonstrate with two in vivo models that these enzymes can protect aquacultured fish from this pathogen as either a planktonic or intracellular form. Established infectious disease models with Nile tilapia will be used to conduct in vivo experiments to determine the therapeutic potential of novel peptidoglycan hydrolases (PGH) or PGH containing protein transduction domains (PTD) (intracellular treatment) to reduce mortality caused by Streptococcus iniae. Small scale studies will be conducted initially used to evaluate dose and timing of delivery. Once these parameters are established, larger scale replicated experiments will be conducted to determine the therapeutic ability of the novel PGH's. The last stage of the grant will explore the potential ability to feed the PGH's expressed in a yeast system to fish and demonstrate the antibacterial nature of these novel alternatives to antibiotics to control fish disease.