A few years previously (**1892**) was [*The Germ Growers: An Australian Story of Adventure and Mystery*][1], by Robert Potter.  A hostile alien race mutates naturally-occurring Earth bacteria in order to conduct bio-warfare against humanity:

> But this Davelli has lately taken up a line of action against God and man which some of the more powerful of his kind took up ages ago with far wider success; he has established here, and in the inaccessible parts of the Himalayas, and in one or two other places, artificial seed-beds of pestilence. His emissaries gather, from all quarters, germs of natural and healthful growth, and submit them to a special cultivation under which they become obnoxious and hurtful to human nature. And then they sow them here and there in the most likely places, and thus produce disease, death, and disaster among men.

The story is public domain, and available at [Project Gutenberg][2].

  [1]: http://www.isfdb.org/cgi-bin/title.cgi?1948064
  [2]: https://www.gutenberg.org/ebooks/60312