Infection and pathogenecity of Myroides odoratimimus (NIOCR-12) isolated from the gut of grey mullet (Mugil cephalus (Linnaeus, 1758))

• Myroides odoratimimus was isolated from gut of mullet.
• Infection and disease of M. odoratimimus in mullet and zebrafish.
• Infection increased the respiratory burst activity and SOD activity in mullet.
• Infection increased the TLR9 expression in zebrafish.
• CpG ODN 1668 was found to be an active immunostimulant in zebrafish and mullet.

Myroides sp. are gram negative aerobes and known for its oppurtunistic pathogenicity in humans. In the present study, Myroides odoratimimus isolated from the gut of Mugil cephalus showed potential infectivity to the experimental grey mullet and acted as an ultimate pathogen with significant symptoms. Furthermore, the inoculum isolated from the infected fishes were cultured and the selected colonies were reisolated and reinjected into healthy juveniles of M. cephalus. Characterizations of the re-isolated bacteria were the same as those of the isolated M. odoratimimus from naturally infected mullet. The median lethal dose (LD50) of the bacteria was 3 × 106 CFU fish-1. In order to assay the accuracy of infection, the production of reactive oxygen species (ROS), the respiratory burst activity of blood leukocytes of mullet before and after challenge was measured, an indicator of the innate immune system. The mullet infection increased the respiratory burst activity and superoxide dismutase activity. In addition, the innate immune response of TLR 9 expression against M. odoratimimus infection and CpG ODN treatment in disease model, zebrafish confirms the M. odoratimimus infection and pathogenicity.