This study compares the effects of two Lactobacillus strains, highly adhesive Lactobacillus brevis JCM 1170
(HALB) and less-adhesive Lactobacillus acidophilus JCM 1132 (LALB), on the survival and growth, adhesive
gut bacterial communities, immunity, and protection against pathogenic bacterial infection in juvenile
hybrid tilapia. During a 5-week feeding trial the fish were fed a diet containing 0 to 109 cells/g feed of the
two Lactobacillus strains. Samples of intestine, kidney, and spleen were taken at the start and at 10, 20,
and 35 days for analysis of stress tolerance and cytokine gene mRNA levels and to assess the diversity of
adhesive gut bacterial communities. A 14-day immersion challenge with Aeromonas hydrophila NJ-1 was
also performed following the feeding trial. The results showed no significant differences in survival rate,
weight gain, or feed conversion in the different dietary treatments. The adhesive gut bacterial communities
were strikingly altered in the fish fed either the HALB or the LALB, but the response was more
rapid and substantial with the adhesive strain. The two strains induced similar changes in the patterns
(upregulation or downregulation) of intestinal, splenic or kidney cytokine expression, but they differed in
the degree of response for these genes. Changes in intestinal HSP70 expression levels coincided with
changes in the similarity coefficient of the adhesive gut bacterial communities between the probiotic
treatments. The highest dose of the HALB appeared to protect against the toxic effects of immersion in
A. hydrophila (P < 0.05). In conclusion, the degree to which Lactobacillus strains adhere to the gut may be
a favorable criterion in selecting probiotic strain for aquaculture.