Subgingival microflora and periodontal disease

Abstract This article describes the subgingival microflora of the healthy periodontium, gingivitis, advanced adult periodontitis, and juvenile periodontitis. A total of seven to nine subjects were examined in each of the four periodontal clinical entities listed. The individual bacteriological samples included material from the base of a single periodontal pocket. The sampling, the treatment of the samples, and the bacteriological cultivations were carried out using continuous anaerobic techniques. Briefly, the healthy gingival sulcus harbored a scant microflora dominated by Gram‐positive organisms (85%), usually Streptococcus and facultative Actinomyces species. The development of gingivitis was accompanied by a marked increase in the total number of Gram‐negative organisms. Fusobacterium nucleatum, Bacteroides melaninogenicus ss. intermedius, Haemophilus species, and other Gram‐negative organisms comprised about 45% of the total gingivitis isolates. Streptococcus and facultative and anaerobic Actinomyces species constituted the majority of the Gram‐positive gingivitis isolates. The micro‐flora of advanced adult periodontitis was comprised mainly of Gram‐negative anaerobic rods (about 75%), B. melaninogenicus ss. asaccharolyticus and F. nucleatum being the most predominant isolates. The deep pocket microflora in juvenile periodontitis was also made up mainly of Gram‐negative organisms (about 65%), but was of a nature different from that of adult periodontitis, being predominated by isolates of Bacteroides species and other organisms of unknown species. The present article also concerns factors of importance for the colonization of Gram‐negative anaerobic rods in the oral cavity and periodontal pockets. In vitro experiments showed that cells of B. melaninogenicus ss. asaccharolyticus and other Gram‐negative organisms attached in high numbers to epithelial cells, hydrosyapatite (HA) surface, and Gram‐positive bacteria when suspended in phosphate‐buffered saline; however, the bacterial attachment to epithelial cells and HA was strongly inhibited in the presence of human saliva and serum. In contrast, saliva and serum had little effect upon the attachment of Gram‐negative bacteria to Gram‐positive bacterial cells. These findings agreed well with data from an in vivo study, in which streptomycin‐labeled cells of B. melaninogenicus ss. asaccharolyticus were introduced into the mouth of two volunteers. A significantly higher number of B. melaninogenicus cells was recovered from dental plaque than from the other oral surfaces studied. The present series of studies has pointed to certain Gram‐negative organisms as potential pathogens in rapidly progressing periodontal lesions. The available data on oral microbial ecology suggest that the presence of dental plaque containing Gram‐positive organisms may be essential for the attachment and colonization of several Gram‐negative species after their initial introduction into the mouth and the periodontal pocket area. The clinical relevance of these findings is discussed.