Spherical forms of Leptospira interrogans serotype canicola Hond Utrecht IV were induced with 1 M NaCl. Electron micrographs of these salt-altered cells (SAC) revealed that the outer envelope or sheath had pulled away from the protoplasmic cylinder. Treatment of SAC with 0.02%7; sodium lauryl sulfate solubilized the sheath and released the protoplasmic cylinder. Further processing of the solubilized sheath yielded a pellet which displayed a membrane structure in electron micrographs. The released protoplasmic cylinder showed loss of intracellular organization and the outer envelope present in normal cells. Immunization of hamsters with whole formalized cells, SAC, or sheath in doses as low as 10 ,ug,'animal

The immunogenicity of leptospiral whole cell (WC) and outer envelope (OE) vaccines from virulent and avirulent strains was compared in hamsters. The 50% protective dose against death (PD,OD) and kidney infection (PD,OK) was evaluated for serotypes icterohaemorrhagiae, canicola, pomona, and grippotyphosa. The OE and WC of virulent strains possessed greater immunogenicity than the OE and WC of avirulent strains. More vaccine (<0.1 to 11.0 jg [dry weight] per hamster) was required for the PD,OK than for the PDIOD (<0.1 to 1.7 gg [dry

Studies were designed to characterize ethambutol uptake by Mycobacterium tuberculosis (H37Ra) and to relate uptake to the time-dependent, concentrationindependent nature of growth inhibition by ethambutol. When cells grown aerated at 37 C in Sauton medium were exposed for 7 hr to 0.2, 0.5, 1.0, 2.5, and 5.0 ,ug of 14C-ethambutol per ml, uptake increased with time and was a linear function of concentration. The process was inhibited at 22 C. Studies with chloramphenicol, sodium azide, and 2,4-dinitrophenol indicated that uptake is independent of requirements for protein synthesis and energy. The organism did not accumulate ethambutol against a concentration gradient. It can be concluded that ethambutol enters the cells in a passive manner. Kinetic studies of 14C loss from tubercle bacilli pretreated with labeled drug suggested the existence of two ethambutol fractions within the cell: a highly variable labile pool and a second fraction that is small and quite firmly bound. Levels of cell-bound drug may be independent of total uptake, but this possibility was not established unequivocally. Definitive evidence showing identity in the concentrations of bound drug regardless of total uptake could explain the apparent discrepancy between concentration-dependent uptake and concentration-independent growth inhibition.

Sodium pyruvate (100 μg/ml) is a useful addition to the Tween 80-albumin medium for the cultivation of parasitic serotypes. It is most effective in promoting growth from small inocula and growth of the nutritionally fastidious serotypes.