Isolation and some properties of Streptococcus mutans AHT mutants with varying adherence abilities.

Abstract

Tenacious glucans synthesized from sucrose are responsible for the attachment of Streptococcus mutans to smooth tooth surface. This paper describes different types of mutants derived from S. mutans AHT (WT), carrying varying degrees of ability to adhere to smooth glass surface.WT was treated with nitrosoguanidine by a method commonly employed. Twenty five mutants were isolated and distinguished into 5 types according to their adherence ability in sucrose medium and colonial morphology. The mutants classified in type M1, M2 and M13 lost their ability to form adhesive microbial deposits. Mutant of type M9 produced a small quantity of strongly adherent, while type M35 mutants formed a extremely large mass of loosely adhering deposits on glass surface. The wire plaque-forming abilities of mutants of each type coincided well with the glass surface-adhering abilities of their own.As compared with WT, type M2 and M13 mutants decreased, while type M1, M9 and M35 increased in the activity of glucosyltransferase produced in a glucose broth. The synthesis of extracellular, water-soluble glucan from sucrose became larger in a quantity in mutants of alltypes, particularly of type M1. and M35. The production of 1N NaOH-soluble, cell-associated glucans of type M1, M2 and M13 mutants decreased to a large extent, but those of type M9 and M35 did not alter from that of WT. Glucose-grown cells of almost all mutants, even of adherence-defective ones, were agglutinated in the presence of sucrose, dextran and various preparation of glucans.These results indicate that the synthesis of alkali soluble, cell-associated glucan in a certain quantity is responsible for the adherence of S. mutans to smooth tooth surfaces. The possibilties were also suggested that some of these mutants might be used to elucidate virulence factor (s)of cariogenic S. mutans.