The production of antibiotics by streptococci

From raw and pasteurized milk and cheese, human, bovine and pig faeces, human nose and throat swabs, 553 pure cultures were isolated and tested by a cross-streak technique on agar. From the same sources, but without isolation and purification of the cultures, 510 samples were also tested by spotting individual colonies with a test-organism culture of Streptococcus agalactiae . A further 8016 samples were tested after enrichment by a quick assay using Str. cremoris as the test organism. The samples examined failed to reveal antibiotic producing streptococci with the exception of some strains of Str. lactis which produced nisin.