In vitro lytic potential of Streptococcus bacteriophage against multidrug resistant Streptococcus agalactiae

Streptococcus agalactiae stands out as a significant bacterial pathogen, causing substantial economic losses in the aquaculture sector. Given the challenges posed by multidrug resistance, this study explores the potential of phage therapy as an alternative to antibiotics in biocontrol strategies. The focus is on evaluating the multidrug resistance profile of S. agalactiae isolated from a tilapia aquaculture farm, with particular attention to the strain KSA/01, which exhibits resistance to seven structurally different classes of antibiotics and a notable MAR index of around 0.6. In response to this challenge, the study successfully identifies and isolates the specific and lytic phage SAP-13 targeting the multidrug-resistant strain KSA/01. Transmission electron microscopy reveals that SAP-13 shares morphological characteristics with the Siphoviridae family. In a one-step growth curve, the phage demonstrates a substantial burst size of approximately 610 PFU/cell over a short burst period and the phage exhibited stability across various physicochemical parameters such as temperature, pH, and salinity. In vitro lytic ability of SAP-13 at different multiplicity of infection underscores its potential to effectively eliminate S. agalactiae, particularly at an MOI of 0.01. Consequently, these findings suggest that phage SAP-13 exhibits high infectivity against S. agalactiae, presenting a promising avenue for addressing multidrug-resistant strains in aquaculture.