VARIATION IN CULTURAL, MORPHOLOGICAL, BIOCHEMICAL-PROPERTIES AND INFECTIVITY OF AUSTRALIAN ISOLATES OF DERMATOPHILUS-CONGOLENSIS

Recent vaccination studies with Dermatophilus congolensis showed that variation of challenge strains had a considerable influence on protect ion afforded by the vaccines. In this study cultural, morphological an d biochemical properties of 30 D. congolensis isolates from throughout Australian were investigated. The infective dose required to produce lesions of equivalent severity by these isolates for sheep, rabbits an d guinea pigs was also examined and the isolates were grouped into fou r clusters of similar infectivity ranking. Analysis of the relationshi p between cultural, morphological and biochemical characteristics and infectivity rankings of clusters was undertaken to determine if certai n properties were linked to infectivity. Considerable variability was found in haemolytic activity on blood agar, mucoid nature of colonies, motility, flagella density and polarity, capsule width, restriction e nzyme profiles of bacterial DNA, protein electropherotype, carbohydrat e content, and enzymic activity against proteins, maltose, chondroitin -4-sulphate, phospholipids and lipids. Of these properties haemolytic activity and enzyme activity against casein, chondroitin-4-sulphate an d lipids showed some link with infectivity ranking for these isolates.