Isolation and Mode of Action of a Staphylococcin-like Substance Active Against Gram-positive and Gram-negative Bacteria

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Abstract
Screening of non-phage group II Staphylococcus aureus strains for antagonistic substances revealed that strain D91 excretes a substance with a wide spectrum of activity; gram-positive and gram-negative bacteria were susceptible. The staphylococcin-like substance D91 produced by this strain was partially purified by column chromatography on Sephadex G-50, DEAE-cellulose, phenyl Sepharose CL-4B and Sephadex G-200. A MW of 76,000 was estimated by gel filtration. The activity was heat sensitive but was not affected by hydrolytic enzymes except for pronase. The protein character of substance D91 was confirmed by gel electrophoresis and subsequent staining with Coomassie blue. The action exerted on sensitive bacteria was bacteriostatic rather than bactericidal. Biosynthesis of DNA, RNA, protein and polysaccharides were inhibited simultaneously in Escherichia coli and S. aureus. Active transport of glutamic acid was stopped in S. cohnii and E. coli; glucose uptake was inhibited in E. coli only. The substance induced a slow efflux of 86Rb+ from proloaded cells of S. cohnii and E. coli. The antagonistic activity of S. aureus D91 was eliminated by ethidium bromide at a rate of 47.6%, suggesting that plasmids may be involved in its production.