See this URL: http://www.answersingenesis.org/articles/arj/v1/n1/microbes-days-of-creation
First paragraph of the abstract:
Microbes and the Days of Creation
by Alan L. Gillen
January 16, 2008
The world of germs and microbes has received much attention in recent years. But where do microbes fit into the creation account? Were they created along with the rest of the plants and animals in the first week of creation, or were they created later, after the Fall? These are some questions that creation microbiologists have been asking in recent years. Ongoing research, based on the creation paradigm, appears to provide some answers to these puzzling questions. The answers to these questions are not explicit in Scripture, so the answers cannot be dogmatic. However, a reasonable extrapolation from biological data and Scripture can be made about the nature of microbes in a fully mature creation. This article attempts to provide reasonable answers to when microbes were created and is meant to stimulate discussion and further research in this area.