Wood is nature’s creation. It supplies a self-cleaning capability that cannot be mimicked in plastic. Studies have shown that compared to plastic, wood cutting surfaces have the ability to self-clean within minutes. Even when plastic cutting boards are placed in the dishwasher at high temperatures, studies have demonstrated that not all of the bacteria is removed. Additionally, because plastic cutting boards develop surface knife scarring, the created nooks and crannies are ideal places for germs and bacteria to hide.
Below are some links that prove the information above to be correct.
Wood Wins- Science News http://www.rhtubs.com/wood-bacteria.htm
Plastic and Wooden Cutting Boards – Dean O. Oliver, Ph.D.
http://faculty.vetmed.ucdavis.edu/faculty/docliver/Research/cuttingboard.htm
Cutting Boards – Chopping Blocks – Butcher Blocks – What’s Cooking America http://whatscookingamerica.net/CuttingBoards/AllAbout.htm