Evaluating the relationship between acidogenicity and acid tolerance for oral streptococci from children with or without a history of caries

Background: Dental caries etiology is attributed to a dysbiotic imbalance within the plaque microbiome leading to a dominance of strong acidogens. Some studies that investigate the link between acidogens and caries quantify the recovery of acid tolerant strains on acid agar as a measure of acidogenic potential. This methodology assumes that acidogenic potential and acid tolerance are directly related. Aim: The validity of that assumption was investigated by statistically evaluating that relationship using streptococci recovered from children with or without a history of dental caries. Methods: Thirty streptococcal isolates were isolated from each of 13 subjects. Acidogenicity was quantified by measuring the terminal pH after overnight growth in Brain Heart Infusion (BHI) and Chemically Defined Medium (CDM). Acid tolerance was quantified by measuring the lowest pH acid agar displaying growth. Results: A significant difference in acidogenicity in CDM between levels of acid tolerance was found, but no significant difference in acidogenicity in BHI was noted. Moreover, there were no significant interactions between acid tolerance and caries history on acidogenicity measures in either medium. Conclusion: An ability to grow on acid agar below pH 5.0 is best aligned with strong acidogenicity and best able to distinguish between subjects with differing caries histories.