Virulence factors of Phocoenobacter atlanticus subspecies atlanticus: in search of vaccine targets.

Pasteurellosis caused by Phocoenobacter atlanticus subsp. atlanticus has a serious effect on Atlantic salmon welfare and the Norwegian aquaculture industry. Understanding the mechanisms underlying bacterial virulence through bioinformatic and functional analyses is an important contribution to vaccine development and prevention of disease. The genome of a clinical isolate of Ph. atlanticus subsp. atlanticus was sequenced and through in silico analysis 16 proteins were predicted to be adhesins, which are known virulence factors and may serve as potential vaccine targets. Expression levels of two such adhesins, a maltoporin-like protein and a 47 kDa outer membrane protein (Omp47), were studied following broth culture of the bacteria at 15°C, 20°C and 30°C and found to increase significantly over time during exponential growth phase from 20°C and higher (Omp47) and at 30°C (maltoporin). This could reflect field observations indicating higher frequency of pasteurellosis outbreaks following thermal delousing treatments. Further research on these target proteins may provide an important basis for development of vaccines against pasteurellosis in Atlantic salmon.