Isolation and characterization of a novel probiotic bacteria Staphylococcus species from indigenous sea bass, Lates calcarifer and evaluation of its probiotic potential in pacific white shrimp, Litopenaeus vannamei

Abstract

In the present investigation, bacterial strains were isolated from the intestinal tract of the Asian sea bass (Lates calcarifer) and screened for potential probiotic characteristics. L. calcarifer was collected from the river Penna, Nellore, Andhra Pradesh, Nellore. Bacteria was extracted from fish intestine using standard protocols and characterized by using gram staining, molecular and biochemical analysis. Among the 27 isolates exhibiting γ-hemolytic activity, only two strains demonstrated high cell surface hydrophobicity, a key attribute associated with probiotic adhesion and colonization ability. Among them, strain LCF15 (the 15th isolate) displayed superior hydrophobicity and was therefore selected for subsequent evaluation of probiotic efficacy.Molecular identification based on the sequence analysis and BLAST comparison, these isolates shared close similarity to Staphylococcus sps. The immunomodulatory capacity of LCF15 strains was investigated in white shrimp (Litopenaeus vannamei) following experimental challenge with Vibrio harveyi. To accomplish this task, two probiotic feed concentrations (1 × 10⁴ and 1 × 10⁶ CFU g⁻¹ feed) were prepared using LCF15 and were administered to control and infected shrimps. Compared with infected control groups, shrimp receiving probiotic supplementation exhibited markedly lower mortality rates. Furthermore, probiotic treatment resulted in significant improvements in several innate immune parameters, including total hemocyte count, phenoloxidase activity, phagocytic activity, and lysosomal activity. These immunological responses showed a clear dose-dependent pattern, with shrimp receiving the higher probiotic concentration exhibiting stronger immune stimulation. Taken together, the results suggest that LCF15 possesses promising probiotic properties capable of enhancing immune function and increasing resistance to pathogenic infection in shrimp and might be used as a tool for promoting health and sustainability in shrimp aquaculture systems.