Colonial Growth of Anaerobic Spirochetes on Solid Media

Hardy, Paul H., Jr. (The Johns Hopkins University School of Medicine, Baltimore, Md.), Young C. Lee, and E. Ellen Nell. Colonial growth of anaerobic spirochetes on solid media. J. Bacteriol. 86:616-626. 1963.-A total of 14 strains of treponemes and one of Borrelia vincentii were cultivated as colonies on agar plates inoculated under ordinary atmospheric conditions, but incubated anaerobically. Every spirochete strain produced diffuse colonies with growth located primarily in the agar; in addition, eight treponeme strains also produced discrete colonies with surface growth. These represented stable colonial variants in several strains, and in one the spirochetes in the surface colonies showed permanently altered cellular morphology. Sufficient variation in colonial morphology was noted between strains to suggest that this may have some value in further classification of this group of microorganisms. Several conditions contributed to the successful growth of all strains as colonies, the most important of which was the use of a firm jelling agar preparation, Ionagar No. 2, that permitted preparation of plates with a final agar concentration of 0.7%. Agar concentrations of 0.9%, or above, in media inhibited treponeme growth.