...we propose, as a first attempt at classification, dividing all microbes into two groups: 1) the free living organosubstrate microbes and, 2) microbes associated with metazoan organisms (Wise pers. comm.). The organism-associated bacteria would not be considered as independent free living microbes but instead as extra-corporeal or extra-cellular organelles and tissues. Thus, humans would not be considered as mosaic creations but as individuals created in the image of God who contain both prokaryotic and eukaryotic cells and tissues.
I'm not sure why they limit it to metazoans (since microbes can be associated with any macrobe), but I like the idea. In the same spirit, I would also suggest that the substrate-associated microbes are actually part of the land, water, wind, etc. Also, it implies that baraminology should be restricted to macrobes, since microbes are properly understood as parts of the things that are visible.
If my information is correct, this article is an introduction to a series of articles in ARJ on microbes. Should be interesting.
Francis and Purdom. 2009. More abundant than stars: an introductory overview of creation microbiology. ARJ 2:85-95.