Mo. Rev. Stat. § 55.100: Appointment of deputies (second class and certain first class counties).

The county auditor, in counties of the first class not having a charter form of government and in counties of the second class, may appoint with the approval of the county commission the deputies that are necessary for the efficient operation of his office. Any deputy shall possess the same qualifications as the auditor and take a like oath of office, and may in the name of his principal perform the duties of the auditor. The auditor and his sureties are responsible for the conduct of any deputy. A deputy shall receive the salary fixed by the county auditor, with the approval of the county commission.