The predominant microflora of nursing caries lesions.

The predominant microflora recovered from infected dentine of 52 carious teeth from 14 children with nursing caries was determined using both selective and non-selective media for the isolation of specific genera and acidified media (pH 5.2) to isolate the predominant aciduric microorganisms, and compared with the microflora of sound enamel surfaces in caries-free children. Streptococcus mutans formed a significantly greater proportion of the lesion flora while Streptococcus oralis, Streptococcus sanguis and Streptococcus gordonii formed a significantly greater proportion of the plaque flora from sound tooth surfaces. The proportions of Actinomyces naeslundii and Actinomyces odontolyticus were significantly greater in the plaque samples than in the lesion samples. Actinomyces israelii formed 18.2% of the flora from the lesions, but was not isolated from the plaque samples. The proportions of Candida albicans, Lactobacillus spp. and Veillonella spp. were also significantly greater in the carious dentine than in the plaque samples. The most frequently isolated lactobacilli were Lactobacillus casei, Lactobacillus fermentum and Lactobacillus rhamnosus. The predominant aciduric flora was S. oralis, S. mutans and A. israelii and these taxa were also isolated from a similar proportion of the lesions at pH 7.0. Strains of S. mutans, L. casei, L. fermentum and L. rhamnosus isolated from individual carious teeth were genotyped using PCR-based methods. Each species was genotypically heterogeneous and different genotypes were recovered from different carious teeth in the same child. These data indicate that the microflora of lesions in the same child is microbiologically diverse and support a non-specific aetiology for nursing caries in which the physiological characteristics of the infecting flora, not its composition, is the major determinant underlying the disease process.