Isolation and antigenic reactivity of Brucella ovis outer membrane proteins

Brucella ovis cell membranes were isolated from fractured and lysozyme-treated cells by ultracentrifugation. These preparations appeared to consist largely of outer membranes, as judged from the results of ultracentrifugation experiments in sucrose density gradients under conditions that are widely used to separate inner and outer membranes of gram-negative bacteria. The sequential detergent extraction of cell membranes yielded mainly lipopolysaccharide and three groups of outer membrane proteins. In immunoblotting, lipopolysaccharide had good antigenic reactivity with all sera from rams exposed to B. ovis (vaccination or natural infection), but some outer membrane proteins reacted strongly only with sera from immune (vaccinated) rams, not from infected rams, suggesting a possible diagnostic role for such proteins in predicting immunity or infection.