For bacterial broth treatments (see below), fresh cultures were generated by adding an aliquot of bacteria to 50 ml of TSY [Tryptic Soy Broth (Difco, Detroit, MI) + 0.5% yeast extract (Sigma, St. Louis, MO)] in a 250 Erlenmeyer flask that was placed on a rotary incubator shaker (Innova 4230, New Brunswick Scientific, Edison, NJ) at 25 C and 130 rpm for 18–24 h