The cultural and biochemical characters of<i>Streptococcus milleri</i>strains isolated from human sources

Abstract

SUMMARY A collection of 346 strains of Streptococcus milleri from a variety of human sources was examined culturally and biochemically, and for the presence of Lancefield group antigens. Most of the strains were non-haemolytic and ungroupable, but 25% were β haemolytic and 19% were α haemolytic; 28% possessed a group antigen (A, 5%; C, 6%, F, 14%, G, 3%). These antigens were present in 69% of β-haemolytic but in only 13% of α-haemolytic or non-haemolytic strains; β haemolysis occurred in 82% of group-F strains, 43% of other groupable strains and 11% of ungroupable strains. The following reactions were given by &gt; 80% of S. milleri strains: hydrolysis of arginine and aesculin, a positive Voges–Proskauer reaction, and acidification of trehalose, lactose, salicin and sucrose. A minority of strains showed enhancement of growth by CO 2 , bile tolerance, NaCl tolerance, and ability to acidify other sugars, notably mannitol, raffinose and melibiose. Departures from the modal pattern of biochemical reactions showed a weak correlation with the type of haemolysis and the presence or absence of a group antigen but were not sufficiently systematic for clear-cut subdivisions to be recognized within the species. S. milleri therefore appeared to comprise a ‘central’ group of non-haemolytic strains that rarely formed a Lancefield-group antigen, in which the aesculin reaction was nearly always positive, lactose was usually acidified, and a considerable minority showed enhancement of growth by CO 2 and bile tolerance. Deviations from this pattern were of two main types. (1) ‘Loss’ of one or more of these reactions, which tended to be associated with β-haemolysis and presence of a group antigen. In these respects, α-haemolytic strains tended to occupy an intermediate position. (2) ‘Gain’ of the ability to acidify additional sugars, notably raffinose and melibiose or mannitol; this occurred mainly among otherwise typical non-haemolytic strains that were rarely groupable. Only 12% of isolations from the bloodstream of patients suffering from systemic infections were β haemolytic and only 18% possessed a group antigen, but a considerably greater proportion of those from visceral abscesses were β haemolytic (28%). Among isolations from superficial lesions in some body sites there were considerably greater proportions of β-haemolytic and groupable strains; thus, nearly one-half of those isolated from the abdomen other than the female genital tract were β-haemolytic and over one-half were groupable. On the other hand, strains from the teeth and gums were nearly always non-haemolytic and ungroupable, and most vaginal isolations were of non-haemolytic strains with a wide sugar-fermentation pattern.