Novel Strategies for the Identification of Soil Bacteria Producing Antimicrobial Compounds

Arlinda Carr, Faiza Aslam, Patricia Porras, Daniel LaMontagne, and Michael Davis, Department of Biomolecular Sciences, Central Connecticut State University

Our lab seeks new antibacterial compounds secreted by soil microorganisms, hypothesizing that some of these may be novel compounds which can serve as antibiotics for treating human disease. We identify such candidate soil bacteria using a crowded plate technique, inoculating solid media with a thousand bacteria and isolating those that form colonies surrounded by a visible no-growth zone. This method has yielded a lab collection of hundreds of candidates for further study, but has limited us to those candidates that inhibit other soil bacteria under the specific plating conditions employed. We have modified this standard screen in several ways designed to identify specialized candidates. One approach applies the existing crowded plate screen but uses medium buffered to pH 3. Fewer soil bacteria form colonies on such media; the proportion of them which fail to grow on standard media is being determined, but is significant. It is hoped that candidates identified with this modified screen will be different from those already in our lab collection. Another approach is directed at discovery of novel antifungal agents, for which there is an increasing need in disease therapy. A screen has been devised which seeds plates with soil bacteria forming colonies within a lawn of yeast cells (Candida). A nonpathogenic surrogate yeast, C. kefyr, is used for the screen, but candidates isolated will be tested for activity against the pathogenic yeast C albicans, and other fungi involved in human disease. Finally, candidates in our existing lab collection are being screened for any with the potential to treat colitis caused by Clostridium difficile, also known as antibiotic-associated colitis. Modifications of our standard screening tests are used to identify candidates with a narrow spectrum of action against clostridia alone. The compounds secreted by such candidates may yield useful new agents to treat this problematic condition.

Presented April 21, 2007 at the 61st Annual Eastern Colleges Science Conference, College of Mount Saint Vincent, Riverdale NY