Halitosis Vaccines Targeting FomA, a Biofilm-bridging Protein of Fusobacteria nucleatum

Abstract

Halitosis (bad breath) is estimated to influence more than half of the world's population with varying degree of intensity. More than 85% of halitosis originates from oral bacterial infections. Foul-smelling breath mainly results from bacterial production of volatile sulfur compounds (VSCs) such as hydrogen sulfide and methyl mercaptan. To date, major treatments for elimination of oral malodor include periodontal therapy combined with antibiotics or antimicrobial agents, and mechanical approaches including tooth and tongue cleaning. These treatments may transiently reduce VSCs but carry risks of generating toxicity, increasing resistant strains and misbalancing the resident human flora. Therefore, there is a need to develop alternative therapeutic modalities for halitosis. Plaque biofilms are the principal source for generating VSCs which are originally metabolized from amino acids during co-aggregation of oral bacteria. Blocking the bacterial coaggregation, therefore, may prevent various biofilm-associated oral diseases such as periodontitis and halitosis. Fusobacterium nucleatum (F. nucleatum), a Gram-negative anaerobe oral bacterium, is a main bacterial strain related to halitosis. Aggregation of F. nucleatum with other bacteria to form plaque biofilms in oral cavity causes bad breath. FomA, the major outer membrane protein of F. nucleatum, recruits other oral pathogenic bacteria such as Porphyromonas gingivalis (P. gingivalis) in the periodontal pockets. A halitosis vaccine targeting F. bacterium FomA significantly abrogates the enhancement of bacterial co-aggregation, biofilms, production of VSCs, and gum inflammation mediated by an inter-species interaction of F. nucleatum with P. gingivalis, which suggests FomA of F. nucleatum to be a potential target for development of vaccines or drugs against bacterial biofilm formation and its associated pathogenicities.