Morphological changes upon subculturing of freshly isolated strains of Leptospira interrogans serovar hardjo.

The morphology of freshly isolated strains of Leptospira interrogans serovar hardjo was studied by electron microscopy and was compared to that of established laboratory strains of the same serovar and to some other serovars within the Hebdomadis serogroup. Changes in the morphology of freshly isolated strains of serovar hardjo were observed when the isolates were subcultured in the laboratory. Cells of strains subcultured more than 20 times were longer and had longer wavelengths, and electron lucent inclusions were observed less frequently than in cells of strains subcultured less than 10 times. Upon hamster passage, cells subcultured 40 and 50 times became more similar to cells of low passage number than to those of the inoculate. The results are discussed and the importance of environmental factors for the growth of leptospires is emphasized.