Mutans streptococci genetic strains in children with severe early childhood caries: follow-up study at one-year post-dental rehabilitation therapy.

BACKGROUND: Genotypic strains of cariogenic mutans streptococci (MS) may vary in important virulence properties. In previous published studies, we identified 39 MS strains from pediatric patients undergoing full-mouth dental rehabilitation, including the removal and/or repair of carious lesions and application of antimicrobial rinse and fluoride varnish. OBJECTIVES: The objectives of this current 1-year follow-up study are to assess the variability of MS strains that occur at 1-year post-rehabilitation and characterize the xylitol-resistance properties of MS strains that predominate. METHODS: Plaque from five children with severe early childhood caries was collected 1-year post-rehabilitation. MS isolates were subjected to arbitrarily primed-polymerase chain reaction (AP-PCR) for identification of genetic strains and in vitro xylitol-inhibition experiments. To more precisely define strain distributions within each patient, we isolated large numbers of isolates per patient. RESULTS: MS strains diminished from several strains pre-rehabilitation, to one dominant strain at 1-year post-rehabilitation, with several new emergent strains. The majority of the clinical MS strains, as well as the Streptococcus mutans laboratory strains ATCC 25175 and 35668, were predicted to undergo 50% inhibition with 2.48-5.58% xylitol, with some clinical MS strains being significantly more resistant in vitro. CONCLUSIONS: Our follow-up study using patients from the original cohort demonstrates that specific MS strains are dominant at 1-year post-dental rehabilitation. Most of the clinical MS strains are similar in xylitol resistance to the attenuated S. mutans ATCC control strains, with some strains being more resistant to xylitol in vitro.

Children with severe early childhood caries: pilot study examining mutans streptococci genotypic strains after full-mouth caries restorative therapy.

PURPOSE: Genotypic strains of mutans streptococci (MS) may vary in important virulence properties and be differentially affected by specific components of full-mouth caries restorative therapy. The purpose of this pilot study was to identify mutans streptococci strains that predominate following caries restorative therapy. METHODS: Plaque from 7 children with severe early childhood caries was collected before and following therapy. MS isolates (N=828) were subjected to polymerase chain reaction (PCR) and arbitrarily primed-PCR (AP-PCR) for assignment within MS strains. Determining the longitudinal changes in MS strain distribution over time within each patient required the isolation of larger numbers of isolates per patient, but from fewer patients. RESULTS: Up to 39 genotypic strains of Streptococcus mutans and Streptococcus sobrinus, and 7 genotypic strains of non-MS streptococci were identified by AP-PCR and 16S ribosomal rRNA gene sequencing. The number of MS strains isolated from each patient were 3 to 7 prior to treatment, diminishing to 1 to 2 dominant MS strains in most patients 6 months following therapy. CONCLUSIONS: Caries restorative therapy resulted in shifts of specific mutans streptococcus and non-mutans streptococcus strains. The implications are that caries restorative therapy affects the distribution of MS strains, and that well-accepted practices for caries prevention should be more closely examined for efficacy.