The typical human mouth contains a writhing orgy of bacteria. Most of these microscopic organisms are benign, and some are even beneficial, but one particular variety is a conspicuous troublemaker: Streptococcus mutans. These ubiquitous bacteria thrive on sugars in the mouth, which they consume while excreting lactic acid. This acid is responsible for the great majority of tooth decay in humankind because it erodes the enamel and dentin of the teeth. A Florida-based company called Oragenics may have found a way to rid our mouths of these acid-excreting organisms for good. This would make cavities a thing of the past, and put no small number of dentists out of business. But despite the obvious benefits, there is potential for disaster. Oragenics’ approach to stopping tooth decay is straightforward: they have used recombinant DNA technology to produce a new variety of S. mutans which does not excrete lactic acid. Instead, it excretes tiny amounts of an agent called Mutacin 1140 which is deadly to other strains of S. mutans, giving these new bacteria an edge over the existing organisms. Once the modified bacteria get a toehold in the mouth, the existing population of S. mutans will be methodically wiped out, leaving the non-acid-producing bacteria in its place. In the absence of acid-producing bacteria, the teeth have little to fear. Oragenics calls this new treatment Replacement Therapy. Photo by Leo-lao protocultor.