Evaluation of antibacterial activity of Pseudomonas species isolated from Pacific white shrimp (Litopenaeus vannamei Boone, 1931) against pathogenic Vibrio spp.

In this research antibacterial activity of Pseudomonas isolates derived from hepatopancreas of Litopenaeus vannamei were evaluated against pathogenic Vibrio spp. Shrimp samples collected from 9 different ponds in Tiab region- Hormozgan province. Hepatopancreas samples of collected shrimps were inoculated in three different isolation media. Pseudomonas Isolation Agar medium revealed highest yield by isolation of an average 22 pseudomonas isolates. Approximately 40 Pseudomonas isolates were obtained. Results of antibacterial screening experiments by well diffusion method demonstrated antibacterial activity of MR21 and MR35 strains. These producer isolates exhibited the highest antibacterial activity against all target Vibrio species consist of Vibrio parahaemolyticus, V. harveyi, V. anguillarum and V. alginolyticus after 72 hours. Biochemical, morphological and physiological studies showed that MR21 and MR35 strains belong to Pseudomonas aeruginosa. Evaluation of antibacterial activity of potent strains in different media proposed trypticase soy broth as an efficient medium. Assessment of temperature influence on antibacterial activity of potent isolates revealed stability of antibacterial activity in 25˚c, 35˚c, 45˚c. Comparison of antibacterial activity of producer strains in presence of seawater and distilled water showed that seawater could promote antibacterial activity. Analysis of growth curve revealed that potent isolates entered to stationary phase after 24 hours. According to achieved results P. aeruginosa MR35 and P. aeruginosa MR21 can considered as potential probiotic isolates for further studies.