TvTO strains of H. piscium were compared for their tolerance to 

 penicillin and streptomycin, H, piscium , strain VIT, tolerated 625 

 units of penicillin but not 1,250. and strain X grew in the presence of 

 5,000 but not in 10,000 units of penicillin. With streptomycin, the two 

 H. piscium strains gave no growth in the presence of more than io units. 



The most rapid and intense fermentation took place in a medium 

 containing glucose, fructose, or sucrose. With these sugars the pH fell 

 below 5.0 within 2 to 3 daysj no gas was formed. Acid was slowly produced 

 from maltose, trehalose, and starch. Weak and slcrw production of acid 

 occurred with mannose, galactose, cellobiose, and dextrin. No acid was 

 produced from arabinose, xylose, rhamnose, lactose, melibiose, raffinose, 

 melezitose, inulin^ glycerol, adonitol, mannitol, dulcitol, esculin, or 

 inositol. 



In media with readily fermentable sugars, growth was rapid and 

 abundant, v/ithout the formation of a ring or pellicle. In media v/ith 

 slowly fermented sugars, growth was also abundant, but usually a 

 pellicle or ring appeared ivithin a week. In the absence of fermentation, 

 growth was moderate with slow formation of a ring or pellicle. Without 

 fish extract, there was a very scant growth and acid production in the 

 basic medium with glucose, fructose, mannose, sucrose, trehalose, and 

 cellubiose. In all cases the results were uniform, and the smooth 

 variants produced somewhat faster growth and more rapid pH changes in the 

 media. 



Under the experimental conditions, the presence of the X and V 

 factors, singly or in combination, was not sufficient for the groTrbh of 

 Hemophilus piscium . It appeared to require some thermolabile substance 

 assumed to be present in potato extract, fish peptone, and rabbit 

 erythrocytes. Rabbit serum would not support growth. Growth was 

 enhanced by the addition of starch to the basal medium containing 

 potato extract or fish peptone. 



Repeated bacteriological examinations revealed that in the 

 infected trout, H. piscium seems to be confined to the ulcerj it can be 

 found in the internal organs, as the blood and kidney, only in the 

 advanced stages of the disease. B. salmonicida, on the contraiy, is 

 present in the kidney and blood from the earliest stage of the infection. 

 Additional pathogenicity tests were conducted on tadpoles and bluegill 

 sunfish. All inooulated tadpoles and sunfieh survived, indicating that 

 the H. piscium was pathogenic to trout only. 



Since several different organisms have been reported from fish 

 with ulcer disease, the evidence therefore suggests that this disease 

 can be caused by a number of different bacteria rdiich behave in fish 

 in a similar manner. The predominating organism of ulcer disease may 

 vary mth the individual hatchery or even vri-th broad geographical 

 regions. Snieszko and associates (1951) for example, have shown that 

 H. pisci-um is the causative agent in the eastern United States. The 



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