Having no issue with microevolution would be great if that meant the Creationist microbiologists think the same thing as non-Creationist microbiologists. Except that isn't the case.
My admittedly cursory understanding of where Creationists and non-Creationist scientists disagree in terms of microevolution has to do with where genetic variation comes from. Creationists think that all genes that exist or ever will are already present in nature. Whereas non-Creationist scientists understand that genes can mutate and new alleles are possible. For example, a Creationist would say that a strain of bacteria that has allele A cannot turn into a strain of bacteria that has Allele B (instead of A). Secondly, they say that Allele A can be transferred horizontally between bacteria strains but its origin is ancient, and that there is no way allele A did not exist at some point in the past because God created it 6000 years ago.
A non-Creationist scientist would say that allele A can evolve into allele B because it can mutate. For example, methicillin-resistant
Staph. aureus picked up the methicillin resistance gene from bacteria called
S. scuri.[1] But S. scuri does not have methicillin resistance. This means the gene changed form, or evolved, when it transferred.
[1]
Development of Methicillin Resistance in Clinical Isolates of Staphylococcus sciuri by Transcriptional Activation of the mecA Homologue Native to the Species
http://jb.asm.org/content/185/2/645.full?view=long&pmid=12511511
You can read more on this well-written blog post which is where I found my example:
http://scienceblogs.com/mikethemadbiologist/2006/06/21/antibiotics-creationism-and-ev/