Creating the attenuated mutant strains of Photobacterium damselae

Abstract

A bacteria strain signing T4.3, having the morphological, physiological and biochemical characteristicsof P. damsalae was isolated from the Pasteurellosis infected fish. It was used to createthe attenuated bacteria strains by ultraviolet (UV) and rifampicin. Applying these factors, 162 modified clones, including 112 clones were generated by UV and 50 clones were obtained by rifampicin. By screening on the sheep blood agar medium, 6 bacteria strains without causing haemolysiswere obtained. Of which, 4 bacteria strains namely T4.3K6, T4.3K7, T4.3K8.1, T4.3K8.2 were created by rifampicin, 2 bacteria strains namely T4.3U5, T4.3U6 were created by UV. These bacteria strains were used to evaluate the ability of causing disease in grouper in order to prove their virulence reduction. The studied result showed that 02 strains (T4.3K8.2, T4.3U6) were safer than 04 others. The survival rate of fish just after infection with dose of 104, 105, 106 CFU/ml of T4.3K8.2 and T4.3U6 was 93.33%, 83.33%, 83.33% and 93.33%, 93.33%, 90%, respectively. Lethal time of the experimental fish was from 8-20 days with the typical signs of Pasteurellosis, such as anorexia, pale gill, opaque convex ankle and haemorrhagic on the fins.