Samples were serially diluted in phosphate buffered saline and spread on deMan-Rogosa-Sharpe (Difco MRS, Becton Dickinson, Sparks, MD) solid medium with 0.001% (w/v) cycloheximide to suppress yeast growth. Plates were incubated anaerobically at 37 C using the Mitsubishi AnaeroPack system (Thermo Fisher Scientific, Pittsburg PA) or the GasPak EZ System (Becton Dickinson) and strains were purified twice as single colonies and stored at 80 C in 40% (v/v) glycerol in 96-well microtiter plates.