Effectivity of bacteriophage therapy against Streptococcus agalactiae in Tilapia: A systematic review

Abstract

Streptococcus agalactiae infection remains one of the most significant bacterial diseases affecting tilapia, leading to substantial economic losses in global aquaculture. Increasing antibiotic resistance has prompted the need for sustainable and effective alternatives such as bacteriophage therapy. This study aims to systematically review and synthesise the current evidence regarding the efficacy of bacteriophage therapy in controlling Streptococcus agalactiae infections in tilapia. Following the PRISMA 2020 guidelines, a comprehensive literature search was performed across PubMed, Scopus, ScienceDirect, and Google Scholar to identify studies published between 2001 and May 2025. Eligible studies were selected according to predefined inclusion and exclusion criteria based on the PICO framework. Relevant data were extracted on phage morphology, host specificity, growth kinetics, physicochemical stability, and therapeutic efficacy. The methodological quality and potential risk of bias of the included studies were evaluated using the SYRCLE Risk of Bias tool. A total of 6 studies matched with our framework were obtained from 2013 to 2024, describing 10 bacteriophages with potential as therapeutic agents against Streptococcus agalactiae infections in tilapia. All identified phages belonged to the class Caudoviricetes, comprising 7 Siphoviridae, 2 Myoviridae, and 1 unclassified phage. Phages were isolated from several sources, including infected tilapia (3 isolates), rearing pond water (6 isolates), and milk from a mastitis-infected cow (1 isolate). Reported growth kinetics showed burst sizes ranging from 20 to 1,236 PFU per cell, with multiplicity of infection (MOI) values between 0.01 and 0.1. The phages were generally stable below 30°C and at pH around 8. These characteristics and combined with their high host specificity indicate promising potential for phage therapy in tilapia combating Streptococcus agalactiae. The included studies demonstrated a low risk of bias in reporting and attrition domains. However, it remained unclear in selection, performance, and detection domains due to limited methodological details. Bacteriophages from Caudoviricetes reported in this study show promising potential as environmentally friendly options for controlling S. agalactiae infections in tilapia. Future work should focus on standardizing experimental procedures, improving reporting quality, and increasing in vivo testing under real aquaculture conditions.