Acidogenesis and Acid Tolerance of Mutans Streptococci in Carious Lesions

Objectives: Mutans streptococci (MS) represent key microbiological determinants of dental caries due to several cariogenic properties, including acidogenesis and acid tolerance. The objectives of this study are to characterize the acidogenesis and acid tolerance properties of MS genetic strains identified within carious and white spot lesions (WSLs).

Methods:   Dental plaque from children (N=20; ages 3-5) was collected from carious lesions, WSLs and enamel surfaces. MS isolates (N between 10 and 20 isolates) from each collection site were selected on mitis salivarius agar containing bacitracin and subjected to polymerase chain reaction (PCR) and arbitrarily primed-PCR for assignment within genotypic strains.  Isolates were subsequently characterized for acidogenesis based on pH obtained after 3 days of growth in phenol red dextrose (N=4 replicates), and for acid tolerance using an ATP-driven bioluminescence assay measuring viable cells and survival at pH 2.7 versus pH 7.0.

Results:  Nineteen MS genotypic strains were identified, with mean acidogenesis and standard deviation (SD) values of 4.60 ± 0.58 and mean acid tolerance (AT) indices of 0.25.  AT indices are defined by numbers of cells surviving treatment at pH 2.7 divided by numbers of cells surviving treatment at pH 7.0.  For patient HH, genotypic strain HH1 was the dominant strain found within carious lesions and WSLs, and was the most acid-tolerant (AT index = 0.184) of all the HH genotypes.  In contrast, genotype HH2 was found only on non-carious enamel surfaces and had mean acidogenesis and SD values of pH 5.84 ± 0.16.  For patient GG, genotypic strain GG1 found within carious lesions and WSLs had mean acidogenesis and SD values of 4.41 ± 0.01 and an AT index of 0.162.

Conclusions:   In these patients, the dominant MS strains found within carious lesions and WSLs had significant acidogenesis and acid tolerance properties.  Supported by OHSU School of Dentistry.