If you are concerned about bacterial contamination of your kitchen counter top, it looks like stainless steel and granite are the way to go.
 
That’s what a recent study by the Hospitality Institute of Technology and Management at the St. Paul , Minnesota organization that develops educational materials and research for the retail food industry, found. Their study measured the bacteria resistance capacity of six common countertop materials. Each surface was contaminated with e-coli (nearly 2 billion of the microorganisms), washed and rinsed with soap and water and then sanitized with vinegar-and-water solution.  The results are as shows in the table below:
 

Material	Organisms Killed
Stainless steel	85,113,804
Granite	79,432,823
Plastic laminate	498,884
Ceramic tile	293,765
Concrete	32,810
Wood	2,080

 
Dr. Peter O. Synder Jr., who conducted the study, says “we hope our research will help consumers make healthy decisions when selecting a countertop surface for their kitchen.”
 
Source: Today’s + Homeowner Magazine via Building Stone Institute, Nov. 1999