@article{mbs:/content/journal/micro/10.1099/00221287-38-2-197, author = "Crowley, Nuala", title = "The Virulence of Biochemical Variants of Streptococcus pyogenes", journal= "Microbiology", year = "1965", volume = "38", number = "2", pages = "197-210", doi = "https://doi.org/10.1099/00221287-38-2-197", url = "https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-38-2-197", publisher = "Microbiology Society", issn = "1465-2080", type = "Journal Article", abstract = "SUMMARY: Two biochemical variants were obtained from a strain of Streptococcus pyogenes, type 19. One variant, known as ‘starch-positive’, always produced amylomaltase, readily forming starch from maltose. The other variant, known as ‘starch-negative’, did not usually form starch from maltose in the same cultural conditions. The starch-positive variant had low mouse virulence and the starch-negative variant had high mouse virulence. The starch positive variant was avirulent for the rat, but the starch-negative variant had some rat virulence. Both variants had plenty of M antigen in precipitin tests and showed good anti-phagocytic power both in bactericidal tests with human blood and in surface phagocytosis tests with isolated human leukocytes. The mouse virulence of the starch-positive variant was enhanced by casein polypeptide and by human plasma. Starch-positive and starch-negative variants obtained from a type 12 strain also had the same properties.", }