Natural Microbial Compounds May Control Strep and Staph Infections

Scientists searching for natural compounds to control fungi in plants may have stumbled onto new antibiotics that control Streptococcus and Staphylococcus bacteria.

Agricultural Research Service scientists at Lane, Okla., and College Station, Texas, say they have discovered a new family of antibiotic compounds--not related to penicillin--with potent antimicrobial activity. They made their find while looking for microbial compounds to control diseases like root rot of muskmelon and watermelon plants.

The discovery and use of antibiotics like penicillin against infectious disease have added about 20 years to the average human life expectancy in developed countries. However, today, up to 80 percent of all strains of Staphylococcus are resistant to penicillin and its derivative forms. Similar resistance to penicillin and other antibiotics has been observed in other bacterial pathogens, like Streptococcus.

The scientists have isolated six compounds that they say exhibit some degree of antibiotic activity against a broad spectrum of gram-negative and/or gram-positive bacteria of concern to both agricultural and health professionals. The compounds varied in their selectivity and ability to retard growth or kill important bacterial pathogens.

The chemical makeup of the cell wall--one of the several techniques used to classify bacteria--determines whether a bacteria is gram-positive or gram-negative. Agrobacterium, Erwinia and Pseudomonas are gram-negative bacteria. Bacillus, Micrococcus, Staphylococcus and Streptococcus are gram-positive bacteria.

Three of the compounds exhibited excellent activity against the genera Staphylococcus and Streptococcus that cause diseases in humans. The scientists say one of the six compounds exhibited strong antibiotic activity against all seven bacterial species tested. Just 10 micrograms per milliliter totally repressed growth of or killed species of gram-positive bacteria within the genera Micrococcus, Streptococcus, Staphylococcus and Bacillus.

As pathogens develop resistance, new and different antibiotics must be found to replace those currently available. The scientists say that some of their compounds may be as good as or better than commercial antibiotics at resisting bacterial infections and could be of considerable interest to the pharmaceutical industry. ARS is the chief research arm of USDA.

Scientific contact: Benny Bruton, ARS South Central Agricultural Research Laboratory, Lane, Okla., phone (580) 889-7395, fax (580) 889-5783, bbruton-usda@lane-ag.org.