Method: LuxS protein sequences were retrieved from NCBI and HOMD databases by BLAST search, aligned and used to construct a phylogenetic tree. AI-2 production was determined in 34 oral bacterial species, representing five phyla, by measuring light production by a Vibrio harveyi reporter strain. Cell-free culture filtrates from the test strains and the V. harveyi culture were combined at a 1:10 ratio in AB medium and light production was measured. The results were considered positive when the light stimulation was higher than 10% of the wild type V. harveyi culture positive control.
Result: The luxS gene was identified in 578 out of 765 oral strains. 20 of the strains tested promoted light production by the reporter strain. Production of AI-2 was observed in all Streptococcus and Prevotella species tested. The strongest stimulation of light production was observed with supernatants collected from cultures of Aggregatibacter actinomycetemcomitans strain ATCC 43718, Eschericha coli strain NCTC 10418 and Prevotella nigrescens ATCC 33563 T (105%, 170 % and 95% of the positive control respectively). The highest concentration of AI-2 was secreted by bacteria in exponential and early stationary growth phases.
Conclusion: Conserved luxS homologues are widely distributed among oral bacteria. Oral bacteria produce AI-2, at varying levels dependent on the strain tested. The role of AI-2 in biofilm formation and virulence requires further investigation.