Outer membrane protein expression duringin vivocultivation of Vibrio salmonicida

Vibrio salmonicidacultures held in dialysis tubing containers were implanted in the peritoneal cavity of rainbow trout (Oncorhynchus mykiss) for periods of between 2 and 8 days. Implants were inoculated with 1×109 cfu. Bacteria within the implants were found to replicate rapidly during the initial implantation period (1·05×1010 cfu after 4 days), stabilise in number, then decrease (minimum 4·8×107 cfu after 8 days). Escaping bacteria resulted in septicaemic conditions in those fish implanted for 7 days or longer. Bacterial outer membrane protein expression was compared before and after implantation using SDS-PAGE. Expression of three proteins of approximately 99, 90 and 78 kDa, was up-regulated underin vivoconditions byV. salmonicida. Ultrastructural studies using transmission electron microscopy and ruthinium red containing fixatives suggest thatV. salmonicidadoes not produce a capsulein vivo. The results are discussed in relation to vaccine development.