Abstract
Streptococcus milleri were isolated from at least one of seven defined oral sites from all 13 children examined. The streptococci were detected in high frequencies and proportions in both subgingival and approximal plaque. Isolation from softened dentine was infrequent but in relatively high proportions when detected. Ninety-nine pure isolates were finally cloned on MC and blood agar plates. All but one of the rough colony-forming strains on blood agar plates (51 strains) showed spontaneous cellular aggregation in BHI broth. Most strains were non-haemolytic (61), and belonged to API taxon S. milleri II (88) and to biotypes la (31) or IId (44). Two-thirds of the isolates were classified into one of six serotypes, c (1), g (10), h (8), i (43), j (2) and k (1), but only one-tenth belonged to Lancefield groups F (untypeable; nine) or G (serotype k; one). Strains isolated from subgingival plaque were biologically and serologically most variable, five serotypes and seven biotypes being detected therein. Multiple serotypes and biotypes were detected in the mouths of five and seven subjects, respectively. However, five subjects harboured strains of a single serotype and four of a single biotype in more than three oral sites; from three of them all isolates were both serologically and biologically distinct. Serological and physiological characteristics of the isolates from various oral sites of respective subjects were generally small in variation and very particular to individual subjects.