Identification and comparison of macrophage-induced proteins and proteins induced under various stress conditions in Brucella abortus.

Brucella abortus is a facultative intracellular pathogen of cattle and humans that is capable of survival inside macrophages. In order to understand how B. abortus copes with the conditions during intracellular growth in macrophages, the protein synthesis pattern of the bacteria grown inside bovine macrophages has been compared with that of bacteria grown in the cell culture medium by two-dimensional polyacrylamide gel electrophoresis. Approximately 24 new proteins that are not detected in the bacteria grown in the cell culture medium have been induced during intracellular growth in macrophages. In contrast, approximately 50 proteins that were expressed during growth in cell culture medium were completely repressed during intracellular growth. The level of expression of 19 proteins increases while that of 54 proteins decreases during intracellular growth. To understand these results, the protein synthesis pattern of B. abortus during intracellular growth was compared with those during other stress conditions. Under each stress condition studied, several new proteins were induced that were not present during regular growth conditions. Comparison of the protein synthesis pattern of B. abortus during intracellular growth with those obtained under various stress conditions has indicated that the response to intracellular growth was not just a simple sum of stress conditions studied so far.