Surface colonies of Leptospira interrogans.

Observations of colonial growth of Leptospira interrogans serovar pomona, BJ, on soft-agar (1% agar) plates revealed the presence of both surface and subsurface colonies. The organisms from both types of colonies appeared to be similar in motility, morphology, antigenic composition, and pathogenicity. Passage in vivo tended to produce a higher incidence of surface colonies, whereas passage in vitro tended to produce a higher incidence of subsurface colonies, suggesting the importance of environmental factors in determining the type of colony produced.