Does Granite harbor bacteria?
Granite Harbors Less Bacteria than Composition Stone

In March of 2004, an experiment was conducted to determine how cleanable certain surfaces are in terms of removing E.Coli Attc 25922 (non-pathogenic E. Coli species), using soap and water, as is done by most home food preparers.  The experiment looked at three polished samples with an E.Coli germ coating applied evenly across the surface of the stone.  The samples included granite with a sealer, granite without a sealer and composition stone.

An area of 81 square inches of each countertop material was inoculated with 1 mL of the E.Coli ATTC 25922 mixture (approximately 13 billion cells per mL) and washed with a water/Dawn detergent solution.

After the surfaces were washed and rinsed, the total sample area was swabbed to find the mean number of E.Coli cells that had been removed from the sample area.  The results are as follows:

Granite w/ Sealer:  Removed an average 208,930 to 1 E-Coli
Granite w/out Sealer:  Removed an average of 60,256 to 1 E-Coli
Composition Stone:  Removed an average of 53,703 to 1 E-Coli

Conclusion:  The above experiment proves that granite without a sealer is as effective as composition stone in reducing E.Coli ATTC 25922 contamination using a wash-and-rinse process.  Further, this experiment proves that using a granite surface with a sealer, as opposed to a composition alternative, will quadruple the number of pathogens removed from the granite countertop after the wash-and -rinse process.