Lactobacillus spp. as probiotics for prevention and treatment of enteritis in the lined seahorse (Hippocampus erectus) juveniles

Abstract

With the aim of using probiotics to control the enteritis in the lined seahorse Hippocampus erectus, three experiments were carried out. In the first experiment, difference in intestinal microbiota between the healthy and enteritis diseased juveniles was investigated to screen the targeted probiotics to enteritis. The results showed that diseased juveniles were heavily deficient in intestinal Lactobacillus spp. compared with healthy ones. Therefore, three Lactobacillus species of L. acidophilus, L. plantarum and L. rhamnosus were employed in the second experiment to test the preventative effect of Lactobacillus spp. on enteritis. The Lactobacillus spp. was daily administrated to the rearing water containing juveniles and live food (copepods) for 45 days. The survival, growth and intestinal parameters, including Vibrio and lactic acid bacteria, immunocytokines (tumour necrosis factor (TNF)-α, interleukin (IL)-1β, interferon (IFN)-γ and lysozyme (LZM)), and epithelial ultrastructure were analysed on days 15, 30 and 45. The results showed that in the administrated groups, particularly administrated with L. plantarum, the survival and growth, together with the abundance of intestinal lactic acid bacteria, were greatly improved, although no decrease in intestinal Vibrio was noted. IFN-γ and LZM, two cytokines that served as indicators for immune capacity, were at high levels during the whole experimental period. While in the control group, enteritis occurred. During the enteritis occurred period (e.g., day 30), TNF-α and IL-1β, two indicators usually for infection or inflammation, sharply increased, and the abundance of goblet cells reduced. These results confirmed that Lactobacillus spp. has a preventive effect on enteritis, and L. plantarum has a better effect than the other two species. Therefore, different doses (0, 5, 10 and 20 × 108 cfu/L) of L. plantarum were used to treat the enteritis diseased juveniles from an epidemic area in the third experiment. The results showed that in the high doses (10 and 20 × 108 cfu/L) groups, the survival rate (from 20% to >45%) and the abundance of intestinal Lactobacillus (from 0.15% to 2.91%) were greatly elevated, respectively. These results confirmed that high dose of L. plantarum has a treatment effect on enteritis.