Longitudinal Determination of Mutans Streptococci Strain Differences by Pulsed Field Gel Electorphoresis in Orthodontic Patients

Abstract

Results of numerous studies have positively correlated the Dentocult® SM test(Ivoclar Vivadent, Amherst, New York) with conventional plating techniques for the enumeration of mutans streptococci in saliva. However, similar studies have not been conducted on saliva samples collected from patients undergoing orthodontic therapy. The hypotheses to be tested in this study were therefore threefold: first, that the Dentocult system is an accurate and reliable method for the determination of salivary counts of mutans streptococci when used with orthodontic patients; second, that a trend (either a general increase or decrease) in levels of mutans streptococci would be seen in orthodontic patients; and third, that because a new surface is presented due to orthodontic appliances, different strains of mutans streptococci, possibly exogenously acquired, might account for increased levels of mutans streptococci, should an increase be seen. Therefore, isolates of these bacteria obtained before and after therapy were examined by Pulsed Field Gel Electrophoresis (PFGE) for detection of strain differences. Two baseline saliva samples, and a saliva, tooth plaque, and appliance plaque sample at 1,2,3, and 4 months after commencement of full orthodontic banding and bonding were obtained from 26 patients in the Indiana University School of Dentistry graduate orthodontic clinic for bacterial enumeration and PFGE analyses. Dentocult was found to correlate extremely well with conventional plating techniques, utilizing Mitis salivarius agar supplemented with bacitracin (MSB), when salivary levels of mutans streptococci were either extremely high(> 10 6 CFU/ml saliva) (91 % correlation) or quite low ( <10 5 CFU/ml saliva) ( 100% correlation). For salivary levels of mutans streptococci between these limits, the percent agreement was not as substantial (49% correlation). Salivary levels >10 6 CFU/ml saliva of mutans streptococci was used as an indicator of caries risk. An increase in the numbers of patients at risk for the development of dental caries was seen at the 2 month sample collection point. Thereafter, the number of patients at risk decreased, so that at completion of the study, the number of patients at risk for caries development was down to near that observed prior to treatment. Fermentation reactions and PFGE analyses were completed for all baseline saliva samples, and all 4 month saliva, tooth plaque, and appliance plaque samples. Fermentative data indicated that 86/102 (84%) of the samples obtained were Streptococcus mutans, and that there were no Streptococcus sobrinus isolates present. The remaining isolates 14/102 (16%) were not characterized further, and were assumed to be viridans streptococci. Results of PFGE indicated that the same, or no more than two different strains of S. mutans predominated in the saliva and plaque of most of the patients examined.