You may be thoroughly cleaning your knives, but if you’re placing them right back into the knife block you’re re-contaminating it. The knife block is a perfect environment for yeast and mold to grow.
Instead: Clean your knife block regularly. Remove all the knives, turn the block upside down, and shake it to get rid of any crumbs or particles stuck inside. Wash the knife block by hand in warm, soapy water, and use a small brush to scrub the slots. Rinse in cool water, and then sanitize in a mixture of water and bleach.