Abstract
Summary
1) An investigation was made of changes in virulence of L. pomona for hamsters following serial transfers in a fluid medium. L. pomona strain W, which did not initially kill hamsters, later produced a lethal effect. Both strain W and O of L. pomona decreased in virulence (increase in LD50 values) during first 4 medium passages. After 4 to 8 passages in media an increase in virulence was observed. Titrations of subsequent medium passages (12 to 24) of strain W indicated a gradual loss of virulence. 2) In vitro hemolysin production could not be correlated with virulence. An explanation for virulence alterations is proposed and the possible significance of hemolytic activity of leptospirae is discussed.
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