CHLORHEXIDINE SUSCEPTIBILITIES OF MUTANS STREPTOCOCCAL SEROTYPES AND RIBOTYPES

The susceptibilities of 379 clinical mutans streptococcal isolates to chlorhexidine (CHX) were tested by agar dilution according to the stan dards of the National Committee for Clinical Laboratory Standards. Iso lates were obtained from saliva samples of 34 young mothers who had hi gh or moderate salivary levels of mutans streptococci at baseline. Sam ples were collected on three occasions, before childbirth, when each c hild was 6 months old, and 1 year later. Of these isolates, 50% were i nhibited at 1 mu g of CHX per ml, 90% were inhibited at 2.0 mu g/ml, a nd all were inhibited at 4.0 mu g/ml. The MICs for Streptococcus mutan s isolates (serotypes c, e, and f) were lower than those for Streptoco ccus sobrinus isolates (serotypes d and g). In some subjects, the MICs for isolates of the same serotype were different. This phenomenon was studied by ribotyping isolates (n = 45) from selected subjects (n = 7 ). It was found that if there were intraindividual differences in the MICs for isolates of the same serotype, then the ribotypes of these is olates were different. In order to decrease the mutans streptococcal i nfection risk for children, 24 mothers (test group) brushed their teet h periodically with a gel that contained 0.3% CHX digluconate and 0.2% NaF, pH 5.8, between the second and third sampling occasions. The gel was used twice a day for the first 10 days of each month. Development of resistant strains during CHX-NaF gel use was not detected. The ser otype distribution of isolates from the test group after 1 year of per iodic CHX-NaF gel use did not differ from that at baseline. Periodic C HX-NaF gel brushing did not lead to lower salivary mutans streptococca l counts.