The microbiology of primary dental caries in humans

What is the association of specific bacteria with tooth decay and can causation be attributed to any of those bacteria?
1) the central role of the mutans streptococci in initiation of caries of smooth surfaces and fissures of crowns of teeth and suggests their potent role in induction of root surface caries;

2) that lactobacilli are implicated as important contributory bacteria in tooth decay, but their role in induction of lesions is not well supported.

What is the source of infection by cariogenic bacteria?

Molecular/genetic studies of implicated bacteria isolated from humans, randomized-blinded-interventional, and longitudinal studies indicate that mutans streptococci are spread vertically among humans, mostly from mothers to their children.