Potential of Bacteriophage
as Therapeutic Agent against Experimentally Streptococcus agalactiae Infection in
Tilapia (Oreochromis niloticus)
Parichat Phumkhachorn and Pongsak Rattanachaikunsopon
Res. J. Biotech.; Vol. 20(12); 1-9;
doi: https://doi.org/10.25303/2012rjbt01009; (2025)
Abstract
A lytic bacteriophage, PUB 01-1 was isolated from tilapia rearing pond water using
Streptococcus agalactiae UB 01 as a host bacterium. The genome of the phage was
double stranded DNA with a size of about 58 kb. Transmission electron microscopy
revealed that the phage had an icosahedral head of 65 nm in diameter and a long
non-contractile tail of about 270 nm long and 12 nm wide. It was classified as a
member of the family Siphoviridae. All 6 strains of S. agalactiae examined were
sensitive to the phage but the rest of the tested bacteria were not.
The median lethal dose (LD50) of S. agalactiae UB 01 for tilapia (Oreochromis niloticus)
by intraperitoneal injection was 1.58 x 104 CFU/fish. The titer and retention time
of the phage in kidney of uninfected tilapia receiving diet supplemented with 103
PFU/g of diet (diet 1) were lesser than those of uninfected fish receiving diet
supplemented with 108 PFU/g of diet (diet 2). The presence of S. agalactiae UB 01
in fish increased the titer and retention time of the phage in fish kidneys. Diets
1 and 2 could reduce mortality of tilapia infected with S. agalactiae UB01 at a
LD50. Diet 2 resulted in no mortality while 30% mortality was observed in the group
receiving diet 1. These results indicate that phage PUB 01-1 has the potential as
a therapeutic agent for controlling fish disease caused by S. agalactiae.
