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STREPTOCOCCI of the Lancefield group D comprise the enterococci (Sherman, 1937), as well as Streptococcus bovis and S. equinus. Among the former, the species S. faecalis (including var. liquefaciens and var. zymogenes) and S. faecium (including var. durans) are recognised at present (Deibel, 1964). All enterococci are characterised by growth (a) at both 10°C and 45"C, (b) in media with a pH of 9.6 and in media with a NaCl concentration of 6.5 per cent., and (c) in 0.1 per cent. methylene blue milk with subsequent reduction. They also survive 60°C for 30 min. and form ammonia from peptone (Sherman). However, no single criterion is specific for enterococci. Growth is observed in S. bovis, in group-E streptococci (Breed, Murray and Smith, 1957) and in group-Q streptococci (Nowlan and Deibel, 1967) at 45°C and after 30 min. of exposure to a temperature of 60°C; all group-Q and some S. bovis strains (Raj and Colwell, 1966) grow in broth containing 6.5 per cent. NaCl. Group-B streptococci also grow in this medium as well as in Hajna's SF broth (Braunstein, Tucker and Gibson, 1969); and group-N streptococci grow in 0.1 per cent. methylene blue milk (Breed et ul.). Conversely, occasional enterococcus strains may be atypical in one of these characteristics (Papavassiliou, 1962). Ideally, therefore, a spectrum of tests should be used for the identification of enterococci (Deibel), but this would probably overtax the resources of most clinical laboratories.

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