R. W. Harrison

The microbic flora of the dental plaque in relation to the beginning of caries.

The bacterial flora of the oral cavity is one of the most complex to be found in or on the human body. This may be attributed in part, at least, to the variety of environments which may be found in the mouth and to the constant inflow of microorganisms from the air and food. This rich field of investigation has intrigued many workers since the early work of W. D. Miller (1) and a very diverse literature has accumulated. Numerous contributions have dealt with the microorganisms indigenous to the mouth and with changes in the flora related to specific diseased conditions. Most of the reports have been restricted to some part of the flora, usually to a single genus or species. Among those studies having a less specialized viewpoint and making notable contributions to knowledge in this field should be included the work of Kligler on the relationship of bacteria to dental caries (2), of Bloomfield (3) and of Brailovsky-Lounkevitch (4) on the evolution of the oral flora in infants, of Howitt and Fleming on changes in the flora associated with different diets (5) and of Bibby (6) and of Brooke (7) on smears from different areas in the mouth. Little attention has been given by workers in either dental or bacteriological fields to the microbic flora of the dental plaque, in spite of the frequently repeated observation, first made by G. V. Black, that in the earlier stages of the carious process the lesion is always found beneath a plaque composed of bacteria and other microorganisms. These masses are most often found on tooth surfaces which are protected from the normal cleansing mechanisms of the oral cavity and in areas difficult to reach with ordinary dental instruments. The paucity of information in this field of dental research is also partly attributable to the numerous technical difficulties of sampling and cultivation of the small amounts of material available. It seems apparent, however, that a search for the bacterial agent or agents which may be responsible for the earliest stages of the carious process must be made among those microorganisms in and under the plaque. If decay is initiated by local bacterial action the responsible microorganism should be found in plaques covering carious enamel and, conversely, if the relationship is a direct one, should be absent when the surface is found to be caries inactive. Indirect evidence of differences in bacterial flora between caries active and caries free tooth surfaces is found in the work of Stephan (8). He has shown that the pH

Comparative Studies on Lactobacilli Isolated from the Mouth and Intestine

This paper is a report of a series of comparative studies made on lactobacilli isolated in this laboratory from the mouths and intestines of a small group of children and adolescents. The investigation is a part of a general program of study on the nature of the association of these organisms with dental caries. The primary purpose in undertaking this phase of the problem was to obtain information concerning the fate of oral lactobacilli during passage through the alimentary tract. Another, less immediate objective was the assemblage of data which could be used in certain projected phases of the general program, namely, study of the sources from which the oral lactobacilli become implanted in the mouth and examination of the relationship of oral lactobacillus incidence with food habits other than excessive carbohydrate indulgence. The reports of earlier investigators who made comparisons between oral and intestinal lactobacilli contain variable and sometimes contradictory results. Some have presented evidence that these are different microorganisms (1-12), others that they are the same (13-26). During the course of previous studies in this laboratory (27-32) the characteristics of the oral lactobacilli had been found to extend over a considerable range. It had become apparent from these findings that, because of the rather marked differences among the oral lactobacilli, the results of any detailed comparison would depend to a large extent upon which oral strains were selected for study and perhaps also partly upon what intestinal strains were chosen. It seemed probable that these difficulties could be avoided in part, and perhaps entirely, by confining the study to lactobacilli isolated from the mouths and intestines of the same individuals. Hadley and Bunting (24) had made a comparative study of the morphological characteristics of cultures collected in this way but they did pot report data on biochemical characteristics or immunological relationships. Preliminary experiments on this subject were begun in 1938 when approximately 50 cultures of lactobacilli were collected from feces and saliva of 20 children who were available as outpatients of the dental clinics. These cultures, unfortunately, were isolated at irregular intervals because of the infrequency of the visits of some of the children to the clinics and because of the difficulty in getting cooperation from others. With this irregular schedule, by the time cultures had been accumulated in sufficient number to begin the study it had

Sensitization of Rabbits By Intradermal Injection of Heat-Killed Lactobacilli of Human Oral Origin:

Examination of the reported findings of many investigators who have studied the incidence of lactobacilli in the oral cavity reveals that the cultures isolated have usually been regarded as belonging to a more or less homogeneous group, presumably a single species. These organisms have been referred to as Bacillus necrodentalis (1), Bacillus acidophilus odontolyticus (2), Lactobacillus acidophilus (3), and less specifically as oral lactobacilli (4a). While there have been, insofar as the authors are aware, no extensive investigations on the origin of the oral strains, it is usually assumed that they enter the mouth in food. Since more than a score of recognized species have been found widely distributed in a variety of natural and processed foods, it is obvious that a number of species must have frequent access to the mouth. It seems unlikely that many of these could become adapted to existence in the oral cavity, but it may be assumed that some of them can persist for a time at least in food masses trapped between the teeth, in occlusal crevices, and about the gingival margins. Thus, cultures as usually prepared from saliva and other material from the mouth might be expected to contain more than one variety or species of lactobacillus. The presence of lactobacilli in intimate relationship with one or more stages of the carious lesion is recognized by most investigators in this field, and a considerable body of evidence supports the belief that these microorganisms are associated with dental caries. Regardless of the nature of this association (whether causal, merely secondary or even accidental) and entirely apart from the possible or probable roles of the other microorganisms in the disease, it is desirable to determine whether more than one species, a single species, or perhaps only certain types of one species are involved. Satisfactory solution of this question necessarily depends upon the use of characteristics with which the limits of the groups under study can be sharply defined. In the past differentiation has been difficult because of the wide variation in morphology and biochemical activities of these organisms (4a) and because of unsatisfactory results of such immunological reactions as have been applied, namely, the agglutination test (2, 5, 6) and the complement fixation reaction (7, 8). The difficulties encountered are probably due, in part, to the presence in different lactobacilli of common antigenic constituents which in these tests may mask the specific reactions