Materials and Methods

Organisms. Cultures of E. aerogenes (ATCC 13048), S. marcescens (ATCC 8100), S. derby (API 245143), S. epidermidis (ATCC 14460), and S. mitis (PI 519) were maintained on Columbia agar plates. These species of bacteria were chosen because they represent several types of Gram-positive and Gramnegative bacteria. Twenty-four hours before an experiment, 10ml of either tryptic soy broth (TSB) without glucose (Difco, Detroit, MI) or Todd Hewitt broth (THB, Difco) was inoculated from a plate and grown overnight at 37 C. After 24h, the culture was diluted 1: 1,000 into sterile TSB or THB and grown at 37 C in 50-ml Erlenmeyer flasks on a rotary shaker at 150 rpm. Growth times for the second culture varied and were based on when the individual species reached the exponential growth phase. The number of bacteria in the suspensions was measured by serial dilutions in physiological saline solution (PSS) and plating onto