Stimulation of Sporogenic and Nonsporogenic Bacteria by Traces of Penicillin or Streptomycin

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Abstract
Washed spores of 13 cultures comprising several aerobic and anaerobic spp. were seeded uniformly into sterile milk. The inoculated samples were heated at 95[degree]C for 15 min. and cooled after which dist. water dilns. of the antibiotics (penicillin 0.01-0.00001 U./ml., streptomycin 0.05-0.0005 U./ml.) were added. These with the controls which received no antibiotic were incubated usually at 30[degree]C and observed frequently for the first visible indication of growth. Most of the cultures including 2 non-spore-formers, Streptococcus agalactiae and Staphylococcus aureus isolated from bovine mastitis, showed some evidence of stimulation in 1 or more dilns. of each drug. In certain of the sporogenic species stimulation was marked, in others it was not apparent. When the milk was enriched with glucose or yeast extract, stimulation by the antibiotics was usually much less evident or absent. Some of the practical implications of growth stimulation by penicillin and streptomycin are discussed.