The Royal Society published part of Leeuwenhoek's Letter L-040 of 9 October 1676 reporting little animals in infusions

March 25, 1677

A long extract from the letter written on October 9, 1676, reporting observations of little animals in spice infusions, was published in Philosophical Transactions, vol. 12, no. 133. Oldenburg translated it himself, but included less than half of the original. In retrospect, we see this as Leeuwenhoek's most important publication because it introduced the microscopic world.

If indeed it was published in March, then it appeared around the time Grew was failing to reproduce Leeuwenhoek's findings of microbes in infusions and six months before Hooke succeeded.