Lactobacillus plantarum ameliorates stress caused by Pseudomonas aeruginosa infection in Nile tilapia

Pseudomonas aeruginosa is a highly pathogenic bacterium affecting the health of Nile tilapia and its production. Fifty moribund fish were collected from farms with high mortality. The causative agent was identified to be P. aeruginosa, and the median lethal dose (LD₅₀) was found to be 1.44 × 10⁵ CFU/mL at a water temperature of 26.5 ± 1.2 °C. To enhance fish immunity, one hundred and thirty-five healthy Nile tilapia were divided into three groups: control (basal diet), single dose of dietary Lactobacillus plantarum at dose of 1 × 10¹² CFU/kg feed, and double dose 2 × 10¹² CFU/kg feed, where supplemented fish showed significant enhancements of their growth performance, feed utilization, and innate immunity (up-regulating serum antibacterial activity, oxidative burst activity, and phagocytosis). Before infection, the gene expression of interleukin (IL)-1β and tumor necrosis factor (TNF)-α was slightly increased in the head kidney tissue of fish that received dietary L. plantarum, regardless of supplementation dose. Meanwhile, post P. aeruginosa infection, the expression of IL-1β and TNF-α was up-regulated significantly compared to the control. Post-infection, fish supplemented with dietary L. plantarum had a lower mortality rate (MR) (50 %) compared to the control (70 %), providing a 28.57 % relative level of protection (RLP). The Nile tilapia, experimentally infected with P. aeruginosa, showed gasping, decreased food apprehension, and loss of escape reflex.

The Nile tilapia, experimentally infected with P. aeruginosa, had some drawbacks, such as immunosuppressed status, abnormal behavior reflexes, and a high mortality rate that dietary L. plantarum could mitigate. Thus, Nile tilapia diet should be supplemented with L. plantarum at 1 × 10¹² or 2 × 10¹² CFU/kg feed.