Actually,I just saw something on this.
They said the Plastic boards have "tiny pockets" where the
bacteria can grow,but the wooden ones,the grain swells
and eliminates these bacterial caverns.
(oiling keeps the grain tight and swollen)
I think the program was Americas Test Kitchen.
Anyway,I use to have 2 boards,one for meat and 1 for veggies etc.
Now I have 3,a plastic one for fruit/veggies,my old maple board
for meat and a new maple board for poultry only.