Upon the receipt of the recommendation of the Planning and Zoning Commission and protest petitions that may have been submitted, the Board of Aldermen shall consider the application and may approve the recommendations of the City Planning and Zoning Commission or take whatever action it deems necessary. If a proposed amendment is not acted upon finally by the Board of Aldermen within one hundred twenty (120) days after the recommendation of the City Planning and Zoning Commission is submitted to it, such proposed amendment shall be deemed to have been defeated and denied, unless the applicant for such amendment shall have consented to an extension of such period of time. Whenever a proposed amendment is defeated, either by vote of the Board of Aldermen or by reason of the operation of this Section, such amendment shall not thereafter be passed without a further public hearing and notice thereof as provided in this Chapter.