– The susceptibility to chlorhexidine of bacteria in aerobic, facultatively anaerobic and anaerobic isolates from clinical specimens of wounds, urine, saliva, and dental plaque was studied. Agar diffusion tests using 50 μg chlorhexidine discs and agar dilution tests were performed and the MIC values correlated with inhibition zone diameters, Anaerobic plaque strains were isolated and tested by the agar dilution method in an anaerobic glove box. Regression lines obtained for five agar media demonstrated a good correlation between zone diameters and MIC values. There was a broad range of susceptibility to chlorhexidine among both Gram‐positive and Gram‐negative strains. Low MIC values were noted for staphylococci, S. mutans, S. salivarius and E. coli, while strains of Proteus, Pseudomonas and Klebsiella were less susceptible. S. sanguis showed intermediate susceptibility with both low and high MIC values. Among the anaerobic isolates tested, the strains most susceptible to chlorhexidine were Propionibacterium and Selenomonas, while the least susceptible strains were Gram‐negative cocci resembling Veillonella.

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– The effect of topical application of a 1% chlorhexidine gel on the population of S.mutains in dental plaque and saliva was studied in five subjects highly infected with the organism. After treatment for 5 min daily for 14 d, S. mutans was not detected in three of the subjects and counts of 700 colony‐forming units or less per ml of saliva were found in the other subjects. Reappearanceof S. mutans was slow and did not reach pretreatment level until 14 weeks or more after therapy. The proportion of S. saguis in plaque increased temporatrily after chlorhexidine treatment, whereas the population of lactobacilli was unaffected. These observations indicate that short‐term use of chlorhexidine is of value in controlling oral infection of bumans by S. mutans.

– Plaque and saliva samples were obtained twice from 58 children at an interval of 1 year and examined for the prevalence of Streptococcus mutans on Mitis salivarius (MS) and Mitis salivarius bacitracin (MSB) agar. Two types of S. mutans colonies with different colonial morphologies were seen on both media. They were serologically identified as serotypes c/e/f and d/g respectively. The first type, morphogroup c/e/f, had the typical “frosted‐glass” appearance. It was the most prevalent and was found in 97% of the children. The second type, morphogroup d/g, had a creamy marzipan consistency with a dull, granular surface, gray to brown in color and often with some liquid around or on top of the colony. Group d/g was detected in 21 children (36%) and then together with colonies of group c/e/f. Children infected with single or multiple morphogroups of S. mutans generally harbored the same groups 1 year later. There was a significant positive correlation between the proportion of S. mutans in plaque and their numbers in saliva.

In order to assess whether naturally occurring oral lactobacilli have probiotic properties, lactobacilli were isolated from saliva and plaque from children and adolescents, with or without caries lesions. The interference capacities of these lactobacilli were investigated against a panel of 13 clinical isolates and reference strains of Streptococcus mutans and Streptococcus sobrinus, as well as against the subject's autologous mutans streptococci, using the agar-overlay technique. Lactobacillus-mediated inhibition differed significantly between the three subject groups (no caries, arrested caries, or active caries), demonstrating increased inhibition in subjects without present or previous caries experience compared to subjects with arrested caries or subjects presenting with frank lesions. Lactobacilli from subjects lacking S. mutans inhibited the growth of the test panel of mutans streptococci significantly better than lactobacilli from subjects who were colonized. Furthermore, subjects without caries experience harbored lactobacilli that more effectively repressed the growth of their autologous mutans streptococci. Twenty-three Lactobacillus spp. completely inhibited the growth of all mutans streptococci tested. Species with maximum interference capacity against mutans streptococci included Lactobacillus paracasei, Lactobacillus plantarum, and Lactobacillus rhamnosus. Naturally occurring oral lactobacilli significantly inhibited the growth of both test strains of mutans streptococci and the subject's autologous mutans streptococci in vitro, and this effect was more pronounced in caries-free subjects.