Calcifiability comparison among selected microorganisms.

Seven ATCC strains of bacteria were examined for apatite formation in a chemically-defined calcification-supporting medium and also in a metastable calcium phosphate solution. One, E. coli, calcified in both. One, S. aureus, calcified in the solution, but not in the medium. The other five did not calcify in either. The results substantiate the belief that calcification is restricted to certain microorganisms. However, they do not rule out the possibility that a noncalcifiable microorganism has the potential to calcify, and the activity is prevented by a cell component. Additionally, the findings emphasize that determining microbiologic calcifiability only in a calcification-supporting culture medium is inadequate. In culture, an efficient calcium pump might preclude calcification by establishing a cytoplasmic calcium level too low for nucleation activation. Calcifiability assays should be done by incubating minimally-metabolizing freeze-dried cells in metastable calcium phosphate solution.