Melioidosis in animals in north Queensland. 3. Bacteriology

Abstract

The bacteriology of 74 strains of Pseudomonas pseudomallei was studied. All strains had a characteristic earthy odour, showed marked bipolar staining and were motile with a single polar flagellum. When incubated at 37°C all strains grew well on MacConkey agar, nutrient agar, and 10 per cent. sheep blood agar. On incubation at 21°C on nutrient agar and 10 per cent. sheep blood agar and at 42°C on nutrient agar growth occurred but was slower.
Colonial type was variable. Rough and smooth forms and forms intermediate between these two were present.
All strains produced acid in litmus milk with slow digestion of the clot, liquified gelatin, reduced methylene blue, produced ammonia, formed catalase and fermented glucose with the production of acid, but without gas. Indole was not formed by any strains nor was hydrogen sulphide produced. In addition, the methyl red and Voges-Proskauer tests were negative. Growth occurred in the presence of potassium cyanide, in Koser's citrate and Levine's medium. Agglutination did not occur in 1/1000 trypaflavine or 0·4 per cent. or 0·85 per cent. saline. No pigmented colonies were produced.
The strains varied in their ability to ferment lactose, sucrose, maltose and mannite, to reduce nitrate, to liquify Leoftler's medium, to form urease and to grow on SS agar.
There was no demonstrable toxin in 24-br broth cultures. The growth of Ps. pseudomallei was not inhibited by increased concentrations of neutral red, crystal violet or bile salts in MacConkey agar.
In vitro, Ps. pseudomallei was most sensitive to chloramphenicol, Aureomycin and tetracycline and partially sensitive to Terramycin and sulphafurazole.
Forty-three guinea-pigs died from melioidosis following intraperitoneal inoculation with emulsions of pus or tissue, two after inoculation with cultures from muddy water and six after inoculation with broth cultures of Ps. pseudomallei. Invariably these showed abscesses of the liver, spleen and omentum and a peritonitis. Sometimes, also, there were subperitoneal abscesses and abscesses of the lungs and kidneys.