Changes in Strains of Mutans Streptococci Induced by Treatment with Chlorhexidine Varnish

Abstract

Isolates of mutans streptococci were obtained from the dental plaque of ten subjects before and after the subjects had been free of detectable mutans streptococci for a mean period of 14.6 weeks (range, from two to 36 weeks). The mutans streptococci had been rendered undetectable by chlorhexidine varnish treatment. Examination of the restriction endonuclease analysis (REA) patterns of the isolates revealed that all ten subjects had one strain (REA type) after re-appearance of the mutans streptococci that was identical to one that had been present before the varnish treatment. In six of the ten subjects, only one strain was detected both before and after treatment. Each of the other four subjects appeared to gain a new strain after treatment; one of the four appeared to lose one strain, and another, four strains. The ability of strains to persist after the period of undetectability seemed unrelated to their resistance to chlorhexidine or to their ability to exhibit insoluble glucan-mediated adhesion. In the subjects harboring multiple REA types, one-seventh of the tooth surfaces sampled harbored two strains simultaneously, suggesting an inability of either strain to exclude the other aggressively. Overall, the study indicated that every subject receiving chlorhexidine varnish therapy had a primary strain of mutans streptococcus that re-emerged after treatment. In contrast, secondary strains were highly susceptible to being lost or gained.

Identification of mutans and other oral streptococci by random amplified polymorphic DNA analysis

“…2. Letter-labelled isolates identified as mutans streptococci were from dental plaque [17] and number-labelled isolates characterised as S. mutans were from saliva [35].…”

“…They included 25 laboratory strains of mutans streptococci, 15 strains of other streptococci (mostly of oral origin) and 5 other unrelated species. A total of 49 clinical isolates was also studied, as shown in Table 1: 17 were dental plaque isolates (identified as mutans streptococci) from eight patients [17] provided by H. J. Sandham (University of Toronto) and 32 were isolated (characterised as S. mutans) in this laboratory from the saliva of 23 young adults [35]. The strains were kept both lyophilised and cryoconserved at À808C.…”

“…Bacterial cells were cultured at 378C in 10 ml of glucose 0.5%-supplemented TYE medium containing (=L): trypticase (BBL Microbiology Systems) 17 g, yeast extract (Difco Laboratories) 3 g, NaCl 5 g and disodium phosphate 2.5 g. The purity and identity of the cultures used for the experiments were confirmed by Gram's stain, colony morphology on MSA (Difco) and on TYE agar containing glucose 0.5%, sugar fermentation patterns and with the API Rapid Strep test (API Laboratory Products, St Laurent, Canada). No further characterisation of the 45 reference strains was performed and the identity of the 49 clinical strains was established as described elsewhere [17,35].…”

“…{ The source of the bacteria is given when known. § Each of these 17 letter-labelled mutans streptococci isolates had a unique REA fingerprint [17]. k Each of these 32 number-labelled isolates was characterised as S. mutans [35].…”

“…Several molecular typing methods are presently available and some of them have been applied to oral streptococci [14,15]. They include DNA-DNA hybridisation [1,12,14], restriction endonuclease analysis (REA) [16][17][18][19], multilocus enzyme electrophoresis (MLEE) [20], ribotyping, PCR and colony hybridisation with DNA probes [21]. A PCR-based procedure of DNA fingerprinting, called arbitrarily primed PCR (AP-PCR) [22] or randomly amplified polymorphic DNA (RAPD) analysis [23], has been applied to strain identification and typing of oral bacteria [24][25][26][27], oral streptococci [28][29][30] and non-oral streptococci [31][32][33][34].…”