Selective persistence of Propionibacterium species FMA5 following sealing of infected dentinal matrix

The objective of the present study was to test the hypothesis that nutrient deprivation by effective isolation should inactivate causative saccharolytic bacteria occupying carious lesions. Vital maxillary third molar teeth were prepared by removing only the superficial necrotic material, leaving behind infected dentinal matrix, before the cavity was sealed with glass ionomer cement (GIC). Before sealing, lesions were biopsied to provide reference bacterial DNA for microbial analysis. After an interval of 10-12 months, the teeth were extracted and, after careful removal of GIC restoration, the underlying dentine was biopsied again for post-treatment microbial analysis. Microbial diversity for nine taxa in 45 carious lesions, before and after minimal intervention therapy, was quantified by real-time polymerase chain reaction (PCR). Except for Propionibacterium sp. FMA5, Fusobacterium nucleatum and Pseudoramibacter alactolyticus, representation of all other taxa showed reduction in the post-restoration biopsy samples. However, Propionibacterium sp. FMA5 was the only species predominantly detected in 80% of the pre-intervention, 82% of the post-restoration and 73% of the paired pre- and post-restoration biopsy samples. The median bacterial load for Propionibacterium sp. FMA5, lactobacilli and bacteria from the family Coriobacteriaceae was higher than the median bacterial load for the remaining six taxa. Significant reduction in the median bacterial load for lactobacilli was evident in post-restoration biopsy samples, implying effective control by GIC after minimal intervention. However, the median bacterial load for Propionibacterium sp. FMA5 increased in post-restoration biopsy samples. Incorporation of antimicrobial agents effective against Propionibacterium species FMA5 could add to more effective conservative management of advanced carious lesions.