Mo. Rev. Stat. § 229.090: Sales agents — certain persons barred.

No member of a highway board or county commission, and no highway engineer or road overseer shall be the sales agent in the sale to, or purchase by, the state, county or road districts, of road tools, culvert or bridge materials or machinery, or be pecuniarily interested in any contract for the building of any bridge or culvert or for the improvement of any public road to which the county or any road district is a party.