[space_fountain]

So to be specific what you're skeptical of here is that S. mutans can outcompete other bacteria without its ability to generate acid If this engineered version can stay in the mouth it should be able to live in the exact same lesions the non mutated version can right? It should still have all the adaptations to live in a low pH environment. I guess this is an extraordinary claim so it's right to be more cautious than the internet usually is, but that also seems to be an easy thing to test for. You can swab someone's mouth who's taken this and see if they still have the mutated bacteria or if it's been out competed

[tadfisher]

Also keep in mind that this strain was discovered about 50 years ago in a human host (the "grad student" reference). The tech is in mutating it further to prevent adaptation, but the beneficial mutation (secretion of mutacin-1140) appears to be the product of natural evolution.

[yorwba]

The beneficial mutation is not secretion of mutacin-1140, but absence of lactic acid production. Transplanting only the original mutacin-1140-producing strain wouldn't help anyone, since it still produces lactic acid that would destroy your teeth all the same.

david_l_lin upthread is stressing that lactic acid is ordinary Streptococcus mutans' primary defense against other bacteria and it wouldn't be able to survive without it.

The significance of mutacin-1140 is that it provides an alternative means of defense against other bacteria (or maybe offense would be a better word) which potentially makes lactic acid redundant.