Correlation of virulence, susceptibility to leptospiricidal activity test mediated by antiserum plus complement and colonial morphology of five lines of a strain of Leptospira interrogans serovar copenhageni.

Correlation of virulence, susceptibility to leptospiricidal activity test mediated by antiserum plus complement (LAT) and colonial morphology was investigated using five lines of Leptospira interrogans serovar copenhageni Shibaura. Line No. 2, a moderately virulent strain, passaged in guinea pigs for 24 successive times caused occasional death of guinea pigs. Leptospiras recovered from deceased animals were characterized by decreased susceptibility to LAT and predominance of hazy colonies upon culture. Leptospiras recovered from surviving guinea pigs were of increased susceptibility to LAT and grew predominantly in non-hazy colonies. Virulent line No. 1 subjected to passage through liquid medium for 20 successive times resulted in a slight decrease in virulence and slight increase in susceptibility to LAT, but the predominance of hazy colonies upon culture was invariable. The other three lines, Nos. 3, 4 and 5 which have been maintained for more than 10 years by passage through different media respectively, were avirulent, susceptible to LAT and produced only non-hazy colonies.