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Serum sensitivity of field isolates and laboratory strains of Brucella abortus
F C Eisenschenk1, J J Houle, E M Hoffmann
1Department of Microbiology and Cell Science, University of Florida, Gainesville 32611, USA.
Objective:
To evaluate the ability of bovine complement to kill a variety of field isolates and laboratory strains of Brucella abortus.
Design:
The experimental approach was to determine the sensitivity of B abortus isolates to killing by bovine serum, and to document the role of complement in brucellacidal activity.
Sample Population:
Six laboratory isolates and 12 field isolates of B abortus were tested.
Procedure:
The ability of B abortus to survive exposure to undiluted bovine serum for 2 hours at 37 C was assessed. The role of complement in killing was determined by examining the ability of heat (56 C for 60 minutes) and cobra venom factor to obliterate the activity in serum, and by detecting binding of the ninth component of bovine complement to serum-sensitive target cells.
Results:
Isolates of B abortus that were resistant to the bactericidal activity of normal bovine serum were revealed. These included field isolates and laboratory strains. Furthermore, the study confirmed earlier reports that bovine serum-mediated killing of B abortus is caused by the complement cascade.
Conclusions:
Some isolates of B abortus, like other gram-negative bacteria, were resistant to complement-mediating killing. Resistance was associated with smooth colony morphology. Isolates lacking detectable O antigen were serum sensitive.