Isolation and physiological characterization of Streptococcus milleri strains from human dental plaque

Of 271 Gram-positive, catalase-negative, chain-forming cocci isolated from crevicular and supragingival plaques of 22 adults, 71 stains were clustered as Streptococcus milleri by testing 23 physiological characters. Most of the oral S. milleri strains were nonhaemolytic and formed minute smooth colonies on glucose and sucrose agar plates, while some of the clinical strains were alpha-haemolytic, forming rough colonies on Carlsson's MC agar plate as well as carrying the Lancefield group antigens C, F or G. The strains were divided into two biotypes, and further into six subtypes by their abilities to ferment maltose, salicin and/or lactose. Distribution of the varieties according to the haemolytic, colonial and serological properties among the oral isolates generally corresponded to the tentative biological types of S. milleri.