Bacteria employ various signaling systems to communicate and sense their environment. The autoinducer type II (AI-2) signaling system is, however, unique in its widespread presence across the bacterial kingdom, allowing communication within and across bacterial species. The S. anginosus bacterial group is commensal to humans but may also be associated with several life threatening diseases including abscesses and cancer. We identified the presence of AI-2 signal production in the S. anginosus group and several other oral streptococci. To investigate the role of AI-2 production in biofilm formation and antibiotic susceptibility, the luxS gene which encodes the enzyme catalyzing AI-2 synthesis was inactivated in S. anginosus and S. intermedius. The resultant S. anginosus and S. intermedius luxS mutants displayed significant reduction in biofilm formation compared to their wild type counterparts. S. anginosus luxS mutant was significantly more susceptible to several subinhibitory concentrations of ampicillin and erythromycin. Supplementation of AI-2 signals significantly restored biofilm formation in S. intermedius and antibiotic susceptibility in S. anginosus to their wild type levels. Targeting AI-2 signaling in bacteria may provide novel and valuable clinical applications in the future.