Christiaan Huygens began series of observations of microbes replicating and expanding on Leeuwenhoek's

Date: 
February 28, 1678

Using his own single-lens microscope, Christiaan Huygens infused rainwater with pepper, ginger, and later coffee to observe the same little animals that Leeuwenhoek had.

By June 11, he was using water that Leeuwenhoek had sent him.

De diertjes waargenomen die ontstaan in water waarin men gebroken peper gedaan heeft. Het was water dat de heer Leeuwenhoek 3 of 4 dagen tevoren had gestuurd.

Observed the animals that form in water in which broken pepper has been put. It was water that Mr. Leeuwenhoek had sent 3 or 4 days before.

Document: 

Oeuvres Compl├Ętes de Christiaan Huygens, T. XIII, Appendix 11, pages 698 - 719

Dutch translation:

https://adcs.home.xs4all.nl/Huygens/13/micr-XIv.html#26-11-78

Sources