Cytological aspects of antimicrobial antibiosis. II. Cytological changes associated with the exposure of Pseudomonas aeruginosa and Bacillus megaterium to colistin sulfate.

Chapman, George B. (Cornell University Medical College, New York, N.Y.). Cytological aspects of antimicrobial antibiosis. II. Cytological changes associated with the exposure of Pseudomonas aeruginosa and Bacillus megaterium to colistin sulfate. J. Bacteriol. 84:180-185. 1962-Broth cultures of Pseudomonas aeruginosa and Bacillus megaterium were exposed to the antibiotic colistin sulfate. Control (unexposed) and exposed cells were fixed, dehydrated, and embedded in methacrylate. Ultrathin sections were examined in an RCA EMU2-D electron microscope. Two conspicuous cytological changes were noted in P. aeruginosa. The nuclear material was no longer demonstrable in its normal sites, leaving an empty space, and the cytoplasm lost its granularity, becoming homogeneous. In B. megaterium, the latter change was also noted. The nuclear material, however, although no longer demonstrable, did not leave an empty space. Rather, it seemed that cytoplasmic material had engulfed and masked nuclear areas. Cells which showed these changes were nonviable.