Inhibition of Streptococcus mutans by the antibiotic streptozotocin: Mechanisms of uptake and the selection of carbohydrate-negative mutants

Abstract

The antibiotic streptozotocin [2-deoxy-2-(3-methyl-3-nitrosoureido)-D-glucopyranoside], an analog of N-acetylglucosamine (NAG), has been shown to be useful for the selection of carbohydrate-negative and auotrophic bacterial mutants. We have adapted this method for use with the oral pathogen Streptococcus mutans, a gram-positive, aerotolerant anaerobe that uses predominantly carbohydrates as carbon sources for growth. Streptozotocin selectively kills growing cells of S. mutans GS-5, and under appropriate conditions it can reduce the number of viable cells in actively growing cultures by a factor of 103 to 104. However, unlike in enteric bacteria, which take up this antibiotic by a single NAG-specific transport system, streptozotocin appears to be taken up in S. mutans by both a NAG-specific system and a relatively nonspecific system that is also involved in glucose, fructose, and mannose uptake. Combining streptozotocin selection and a screening procedure involving indicator-plates containing triphenyl-tetrazolium chloride, we developed a general method for the isolation of carbohydrate-negative and auxotrophic mutants of S. mutans. A preliminary characterization of both pleotropic and specific carbohydrate-negative mutants isolated by using this procedure is presented.