Each person appointed under Code Sections 35-9-2 through 35-9-5, this Code section, and Code Sections 35-9-7 through 35-9-12 shall, within 15 days after his certificate of appointment has been issued and before entering upon the duties of his office, take and subscribe the oath prescribed by Code Section 45-3-1 and file it in the office of the appointing authority.
OCGA § 35-9-6