Isolation and biochemical identification and evaluation of antimicrobial activity of bacteria isolated from the intestine of marine fishes in southern Iran

Abstract

Introduction: In recent years, the use of dietary supplementation with probiotic bacteria
has been interested in the aquatic farming. The objective of this study was to isolate of lactic
acid bacteria with probiotic potential from the intestine of the marine fish under in invitro
condition and based on probiotics characteristics.
Materials & Methods: For this purpose, marine fish samples weighing 300- 700 gr from
active farms were taken from the marine environment of Bushehr, Hormozgan and
Khuzestan provinces. Bacterial isolates were collected from 50 marine fish intestine. In
total, 10 strains were isolated in MRS agar media. The isolates were evaluated and ranked
based on the probiotic indication tests (bacterial antagonistic property, adhesion abilities to
mucus, growth in intestine mucus, Hydrophobicity, salinity, pH, temperature and bile salt
resistance, Extracellular enzyme production and the lack of pathogencity to aquatic).
Results: The probiotic potency of these 10 isolates was compared and finally 3 isolates
including P1, B6 and L2 were selected as the highest potent probiotic property. The final
identification of the selected strains was done by sequencing of 16 S rRNA gene after
assurance the absence of resistance genes for streptomycin, tetracycline and fluorophenicol
antibiotics. After the sequencing the 3 isolates were identified as strains of Lactobacillus
plantarum, Lactobacillus plantarum and Lactobacillus pentoseous respectively. The
sequences of these isolates had a 99 to 100 percent identity with the nucleotide sequences
published in the Gene Bank database. These strains had the ability to resist in the
temperature of 10 to 37° C, salinity 0 to 30 g ppt and pH 3 to 9 values. Also, these bacteria
had suitable Adhesion to mucus, growth in intestine mucus, Hydrophobicity, antimicrobial
activity against Yersinia ruckeri, Aeromonas hydrophila, streptococcus iniae and
Lactococcus garvieae and were resistant to bile salts. These strains had any enzymes such
as lipase, amylase and protease activity.
Conclusion: Based on the results of this study, after in vivo studies, these isolates can be
used for the purposes of probiotic in aquaculture, especially marine fish culture industry in
the study area.