Before entering upon the performance of his duties, the county highway engineer and his assistants shall each execute and deliver to the county commission a bond in such sum as may be fixed by the commission, with two or more sufficient securities, or the bond of a surety company authorized to do business in this state, to be approved by the commission, conditioned for the faithful discharge of his duties as such highway engineer; and that he will account for and deliver to his successor in office, at the expiration of his term of office, all tools, machinery, books, papers and other property belonging to the county and road districts thereof.