Vibrio spp. Were a cause of serious disease in aquaculture. This study aimed to develop a Vibrio spp. inhibition
method that is safe and friendly for the environment, namely bacteriophage (phage). Vibrio spp. and their phages
were isolated from shrimp, water, and mud from farms in Mekong Delta provinces (Kien Giang, Soc Trang, and Bac
Lieu provinces). Then, the phage influence on the bacterial concentration and the toxR gene was investigated by
comparing the gene sequences pre- and post-infection. The polymerase chain reaction identified 31 strains of Vibrio
spp., including 9 of Vibrio parahaemolyticus. Then, using several isolated Vibrio spp. as hosts, 32 phage strains
were isolated. Results found that each bacteriophage affected the Vibrio toxR gene in specific ways. Phage ST9
and phage ST10 did not change bacterial concentration, but they could change nucleotides at 4 positions compared
to the V. parahaemolyticus sequence. Nevertheless, phage KG6 could reduce bacterial concentration but did not
affect gene sequences. The bacteriophages can affect bacteria through several mechanisms, including reducing the
bacterial concentration via the lytic process or affecting genes encoding bacterial virulence. These findings open a
new direction in phage therapy research if such an effect can reduce or neutralize bacterial virulence.