GROWTH OF XYLITOL-RESISTANT VERSUS XYLITOL-SENSITIVE STREPTOCOCCUS-MUTANS STRAINS IN SALIVA

Five Streptococcus mutans pairs (serotype c S. mutans 10449 and four c linical isolates of S. mutans: 123.1, LG1, OMFA, T10B) were used to fi nd out if the xylitol-resistant (X-R) natural mutants of the correspon ding xylitol-sensitive (X-S) S. mutans parental strains differ in thei r growth patterns in saliva. The isogenic X-R natural mutants of the p arental S. mutans strains were selected after sequential cultivations in the presence of xylitol and glucose. The X-R/X-S strains pairs were growth in individual and pooled glucose-supplemented filter-sterilize d salivas (one to five sequential cultivations). The two salivas used represented subjects with good or poor support of the growth of S. mut ans in vivo. Protease and peptidase activities were determined from th e saliva growth media and cell suspensions. Salivary protein profiles were analyzed using SDS-PAGE and native IEF before and after the culti vations. The growth properties of the X-R/X-S S. mutans pairs were sim ilar in both individual and pooled salivas. Sequential cultivation of all strains did not show any differences in growth patterns. X-S strai ns were inhibited by the presence of xylitol (2% w/v) in pooled saliva , as shown for other glucose-supplemented media. Protease and peptidas e activities of the X-R/X-S S. mutans pairs were low and of similar ma gnitude. Also, the general hydrolytic properties of most X-R/X-S S. mu tans pairs appeared similar as judged by the small growth-induced chan ges in salivary protein profiles. In conclusion, saliva, the source of nutrients for salivary microorganisms in vivo, favored neither the X- R nor the X-S strains of S. mutans.