Re: What bacteria was first viewed?

I do not believe that History has recorded exactly which bacterium was seen by Anton von Leewenhoek when he first peered into his microscope and was astonished to find "wee beasties" living on his slide. There is, however, a delightful reproduction of a page from von Leeuwenhoek's notebook on a site maintained by Professor Michael Womack of Macon State College. The picture shows a variety of what we now know as "bacteria" -- perhaps you can identify some of them from the drawing. It can be found at http://www.faculty.mc.peachnet.edu/mwomack/micro.htm

Moderator's Note: In addition, you might check your public library for a copy of the The Microbe Hunters by Paul de Kruif. He tells the story of Anton von Leeuwenhoek and the "animacules" he discovered with his microscope.

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Admin Note:
James Cotton provided an additional answer:

It seems likely that Antony can Leeuwenhoek managed to see bacteria through his primitive microscopes as early as 1683. Other people may have seen bacteria earlier, but Leeuwenhoek^Òs notes are the first record of it. There is an interesting controversy over Leeuwenhoek's claim to have viewed there organisms. For many years it was generally considered theoretically impossible for the primitive microscopes of the 17^th century to have resolved organisms as small as bacteria (apparently, an examination paper at Aberdeen University even asked students to explain why this was impossible) but experiments using one of Leeuwenhoek's own microscopes have since shown that he would have been able to obtain tenuous images of bacteria. In a passage from 1676, Leeuwenhoek himself explains that while studying a suspension of pepper grains in water, he saw large protozoa and also some organisms that were "incredibly small, nay, so small in my observations that even if one hundred of these very tiny animals were laid end to end, they could not reach the length of a grain of coarse sand".

To see what Leeuwenhoek might have seen of these bacteria through his microscope, visit this page. There is also this web page about the history of microscopy in general.