Aeromonas salmonicida subsp. salmonicida: correlation of protein patterns, antibiotic resistance, exoprotease activity, haemolysis and pathological lesions produced in vivo

A collection of 130 strains of the bacterial fish pathogen Aeromonas salmonicida subsp. salmonicida isolated from diseased salmonids in Denmark, Norway, North America and Scotland has been characterized with regard to protein patterns, antibiotic resistance and exoprotease activity. Whole cell and outer membrane protein profiling could distinguish three different profiles in A. salmonicida. Eight outer membrane proteins were demonstrated (49, 40, 38, 37, 33, 31, 30 and 29 kDa). One protein profile was deficient in a 38 kDa outer membrane protein and instead contained an outer membrane protein of 37 kDa which was not detectable among the other protein profiles. Strains with the 37 kDa outer membrane protein showed multiple low-level antibiotic resistance towards cephalothin, penicillin, chloramp-henicol, tetracycline and quinolones. In addition, these strains were exoprotease deficient. Strains with the 37 kDa protein were unable to degrade cattle and trout serum proteins and displayed a delayed degradation of casein. Haemolysis on cattle blood agar plates was similarly delayed. In vivo examination of extracellular products from a normal protein profile strain and one with the 37 kDa outer membrane protein demonstrated major differences in pathological effects in rainbow trout. The strain possessing the 37 kDa outer membrane protein produced almost no pathological effects while the normal protein profile strain produced typical furuncles.