All stock cultures were stored at 80 C in 0.7 ml of Tryptic Soy Broth (TSB; Difco, Becton Dickinson, Sparks, MD, USA) and 0.3 ml of 50% glycerol. Working cultures were streaked onto Tryptic Soy Agar (TSA; Difco), incubated at 37 C for 24 h, and stored at 4 C.