title: pH gradient and distribution of streptococci, lactobacilli, prevotellae, and fusobacteria in carious dentine.
abstract: OBJECTIVE
  Caries process comprises acidogenic and aciduric bacteria that are responsible for lowering the pH and subsequent destruction of hydroxyapatite matrix in enamel and dentine. The aim of this study was to identify the correlation between the pH gradient of a carious lesion and proportion and distribution of four bacterial genera; lactobacilli, streptococci, prevotellae, and fusobacteria with regard to total load of bacteria.
  
  
  METHODS
  A total of 25 teeth with extensive dentinal caries were sampled in sequential layers. Using quantitative real-time PCR of 16S rRNA gene, we quantified the total load of bacteria as well as the proportion of the above-mentioned genera following pH measurement of each sample with a fine microelectrode.
  
  
  RESULTS
  We demonstrated the presence of a pH gradient across the lesion with a strong association between the quantity of lactobacilli and the lowest pH range (pH 4.5-5.0; p = 0.003). Streptococci had a tendency to occupy the most superficial aspect of the carious lesion but showed no correlation to any pH value. Prevotellae showed clear preference for the pH range 5.5-6.0 (p = 0.042). The total representation of these four genera did not reach more than one quarter of the total bacterial load in most carious samples.
  
  
  CONCLUSIONS
  We revealed differential colonization behavior of bacteria with respect to pH gradient and a lower than expected abundance of lactobacilli and streptococci in established carious lesions. The data indicate the numerical importance of relatively unexplored taxa within the lesion of dentinal caries.
  
  
  CONCLUSIONS
  The gradient nature of pH in the lesion as well as colonization difference of examined bacterial taxa with reference to pH provides a new insight in regard to conservative caries management.
authors.affiliation: Institute of Dental Research, Westmead Center for Oral Health and Westmead Millennium Institute, Sydney, Australia, nima.kianoush@sydney.edu.au.
authors.forename: Nima
authors.initials: N
authors.lastname: Kianoush
authors.forename: Ky-Anh T
authors.initials: KA
authors.lastname: Nguyen
authors.forename: Gina V
authors.initials: GV
authors.lastname: Browne
authors.forename: Mary
authors.initials: M
authors.lastname: Simonian
authors.forename: Neil
authors.initials: N
authors.lastname: Hunter
mesh_terms: D001419:Bacteria / Q000145:classification / Q000302:isolation & purification*; D003731:Dental Caries / Q000382:microbiology*; D003804:Dentin / Q000382:microbiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration