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Mutans Murder Machine: A Targeted Treatment for Dental Cavities

The oral microbiome comprises a variety of both commensal and detrimental microbes. Oral health requires a fine balance of these organisms, which can be upset by broad-spectrum antibiotics. Our experiments involved the use of the peptide based antibiotic actagardine, known to have activity against Streptococci. Homologs of actagardine were also incorporated into the designed gene cluster, in an effort to develop novel antimicrobial compounds. We sought to use synthetic biology tools to create a targeting system for an antibiotic to kill only Streptococcus mutans, the primary causative agent of dental cavities. A combinatorial approach applying phage display and heterologous expression of modified lantibiotics was applied to develop this targeted S. mutans killing machine.


Antibiotics have helped to shape modern medicine and increase life expectancies considerably around the world. Penicillin, the first biologically-derived antibiotic, has saved millions of lives since its discovery in 1942 (1). Hundreds of antibiotics have been developed since then, which target a variety of pathogenic microorganisms. However, due to widespread overuse of antibiotics, antibiotic resistance has become a major obstacle in the treatment of infections with multi-drug resistant tuberculosis and MRSA(5). Combined with a decreasing rate of antibiotic discovery, antibiotic resistance in human pathogens has precipitated a significant crisis in modern medicine.

Due to the limited number of antibiotics remaining on the “front lines” of treatment, there is a need for a novel approach to antibiotic discovery. Lantibiotics are ribosomally-synthesized peptides that incorporate a number of characteristically modified amino acids. They are produced by a number of Gram-positive bacteria, and act to inhibit other microorganisms in competition with them (6). Thus, lantibiotics act as a unique platform for the identification of novel antimicrobial compounds. The mechanisms of action of lantibiotics are poorly characterized, although it is known that they target the bacterial cell wall (6). The peptide nature of lantibiotics renders them particularly amenable for modification by direct genetic manipulation and the potential for the creation of novel antibiotics from existing biological examples is high (6). (Emerson and Sathee: how lantibiotics are produced) (Team Phage Display: Why the oral microbiome? Future applications/foundational advance)

We heterologously expressed the lantibiotic actagardine, which was modified to directly target the Gram-positive pathogen Streptococcus mutan. S. mutans is found in the oral microbiome and is widely regarded as one of the major causative agents of tooth decay (7). Dental cavities affect a significant portion of the global population yearly, and resultant bacterial infections have the potential to spread systemically and cause serious life-threatening health problems. However, the application of common clinical antibiotics in the treatment of S. mutans-related dental cavities is currently limited by their broad-spectrum activity. Antibiotic treatment causes damage to the entire oral microbiome, eradicating commensal organisms important to maintaining good oral health. The application of a targeted antibiotic will be an important step forward in helping to manage the impact of dental cavities worldwide, and our results can be extended to other diseases caused by oral pathogens, including periodontal disease, halitosis and some forms of oral cancer (Dragana ajdic et al, 2002 PNAS)