Effect of Antiseptic Mouthwash on Retention of Oral Streptococcal Strains

The use of oral antiseptic mouthwash has the potential to reduce the carriage of harmful micro-organisms but the effect on the dominant benign (potentially beneficial) organisms and concomitant disruption of the oral ecology has not been assessed.  Objectives: This study aimed to determine the effect of mouthwash containing chlorhexidine on the retention of specific strains of streptococcus, distinguished (typed) by arbitrarily-primed PCR (AP-PCR).  Methods: Five healthy participants undertook a two-week course of mouthwash treatment, rinsing twice daily.  Samples were collected from the lower incisors before mouthwash usage and again on completion of the course.  Samples were cultured on Mitis-Salivarius agar and incubated anaerobically at 37°C for 24 hours.  From each participant, 30 colonies were subcultured (purified) by restreaking onto tryptic soy agar.  Colonies from each subculture were lysed to release DNA that was used as template in AP-PCR.  Amplicon profiles from samples recovered before and after mouthwash treatment were compared for each participant.  Results: Overall the numbers of distinguishable streptococcus strains decreased from mean 11.4 (±3.6) before to mean 8.2 (±2.8) after mouthwash treatment; and the dominant strains changed in four participants.  For two participants, the entire streptococcal profiles changed; thus, none of the strains detected before treatment were detected after treatment.  Only one participant maintained the same dominant strain before and after mouthwash treatment, although the proportion of this strain decreased by 50%.  Conclusions: These findings indicate that the protracted use of mouthwash has a significant effect on the resident oral microbiota of an individual.  Future experiments to expand this trial will include samples recovered three months after completion of the mouthwash to determine whether the original streptococcal strains re-appear in the absence of the antiseptic.