Nalidixic acid (negram) disc technique for the rapid isolation of faecal streptococci from mixed flora.

FAILURE of treatment of urinary infections due to faecal streptococci in association with other bacteria (Garrod, Shooter and Cunven, 1954) has indicated the need for combined antibiotic therapy in these cases (Eisenberg, Alexander and Flippin, 1953). The incidence of streptococci in mixed urinary infections appears to vary from 10 per cent. (Sanford et aZ., 1956) to 22.4 per cent. (Rantz and Kirby, 1943). As could be expected, faecal streptococci were also found with coliform bacilli in gastro-intestinal perforation leading to peritonitis (Rantz and Kirby). The difficulties of recovering faecal streptococci from a mixed flora have been noticed from time to time. Seidman, Ellis and Hill (1929) observed a lack of correlation between the smear and the culture of urinary sediments. Baker (1931) also noted that only Gramnegative organisms appeared in cultures although both Gram-positive and Gram-negative organisms were seen in smears. The possibility of suppression by the predominant organism has been suggested by Flint (195 1) and Giertz and Gullbring (1 951). Gould ( 1 95 1 ) explained the discrepancy by the more rapid growth of the Gram-negative bacilli in a mixed urinary tract infection. As streptococci (except occasional strains) are not inhibited by nalidixic acid in vitro, they can be isolated conveniently from the zones of inhibition of the coliform bacitli on primary culture plates.