Properties of Brucella canis surface antigens associated with colonial mucoidiness

Rough Brucella strains B. abortus (45/20), B. ovis (1182), wild type B. canis (M+) and a less mucoid (M-) variant possessed cell wall antigens that were extracted by both sodium desoxycholate (SDC) and hot phosphate buffered saline (PBS). The acid precipitability of cell wall surface antigens extracted in SDC from all four strains suggests that these antigenic complexes may be responsible for the bacterial aggregation in broth media at acid pH and for the relatively high colonial viscosity on normal agar media (pH 6.8). The antigens of B. canis (M+) extracted in PBS were serologically related to those from the other 3 strains, but they differed in acid precipitation and hydrophobic characteristics. Differences between the properties of B. canis surface antigens and those of the other rough Brucella may explain the highly mucoid nature of the canine organism when grown on conventional (pH 6.8) media.