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Changes in growth rate and infectivity ofLeishmania donovani subjected to various laboratory procedures

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Abstract

Two substrains ofLeishmania donovani strain 3S were used in a study of grwoth rates of promastigote and amastigote stages as well as of infectivity of the latter stages in the course of cultivation, animal passages, and heat adaptation. One of these substrains, 3S-25A, was initiated with amastigotes of strain 3S maintained by serial passages in golden hamsters since 1962. The 3S-25A promastigotes were transferred 24 times (about 142 generations), then passaged once in a hamster. The amastigotes derived from this hamster on postinoculation day 30 were employed for initiation of culture promastigotes designated as substrain 3S-25A′. This culture was transferred 20 times (about 141 generations). The third substrain, 3S-37, was isolated in culture in 1974, then adapted to 37° C. All cultures were grown in modified Tobie's medium (Tm). Young C57BL/6J mice were employed in the estimation of generation times (G) of amastigote stages and infectivity of promastigotes.

Upon isolation in culture, substrain 3S-25A promastigotes grew poorly and inconsistently during the first five transfers (about 20 generations). Between the fifth and 13th transfers (about 20th and 65th generations), the populations increased from 1.9×107 to 1.2×108 organisms/ml. They remained approximately constant until the 24th serial transfer (about 142nd generation) at which time some of the promastigotes were inoculated into hamsters while others were stabilated in liquid nitrogen. The initial increase in the promastigote yields appeared to depend upon decrease inG (from 12 to 7 h). Promastigotes of substrain 3S-25A′ reached the maximum numbers in the primary cultures.

High infectivity was characteristic of the early in vitro transfers of substrain 3S-25A′, 25% for the fifth serial passage (about 30 generations), but the infectivity decreased rapidly on cultivation, reaching a 0.5% level by the tenth transfer (about 100 generations). In contrast, relatively low infectivity levels were observed for 3S-25A promastigotes during the first few passages, e.g., 1.2% for those from cultures obtained after five serial transfers. These levels increased up to the 12th transfer, when they reached 8%. Further cultivation, however, was accompanied by infectivity decrease — after 24 passages in Tm, it was estimated at 4%.

TheGs estimated from counts of amastigotes in livers of hamsters inoculated with substrains 3S-25A and 3S-25A′ were closely comparable; for infections with tenth-transfer promastigotes of these strains, the times were, respectively, 34 and 36 h. On the other hand, theG for amastigotes in livers of hamsters inoculated with strain 3S-37 promastigotes from the tenth serial in vitro passage was much longer, 53 h.

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References

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Correspondence to Lloyd H. Semprevivo.

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Semprevivo, L.H., Yusuf, J.N. & Honigberg, B.M. Changes in growth rate and infectivity ofLeishmania donovani subjected to various laboratory procedures. Z. Parasitenkd. 65, 43–51 (1981). https://doi.org/10.1007/BF00926552

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Keywords

  • Primary Culture
  • Initial Increase
  • Laboratory Procedure
  • High Infectivity
  • 65th Generation