Serum sensitivity of field isolates and laboratory strains of Brucella abortus

F. C. Eisenschenk From the Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

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J. J. Houle From the Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

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E. M. Hoffmann From the Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

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Abstract

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-mediated killing. Resistance was associated with smooth colony morphology. Isolates lacking detectable O antigen were serum sensitive.

Abstract

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-mediated killing. Resistance was associated with smooth colony morphology. Isolates lacking detectable O antigen were serum sensitive.

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