Sodium thioglycolate

AgNO₃, chlorhexidine digluconate, 20% (w/v), HNO₃, ~70% (w/w) were purchased from Sigma-Aldrich. Chemicals for the preparation of the neutralization solution: sodium thioglycolate, sodium thiosulfate, lecithin, were purchased from Acros Organics; Tween 80 (polyethylene glycol sorbitan monooleate) was purchased from Fluka.

Bile tolerance of S. thermophilus and L. bulgaricus was determined by the method of Perei and Gibson (2002) [26 (link)] with some modifications. S. thermophilus (10% (v/v)) was inoculated into M17 broth (Criterion™, Hardy Diagnostics, Santa Maria, CA, USA) supplemented with 0.3% (wt/v) oxgall (bovine bile) (US Biological, Swampscott, MA, USA) to evaluate its ability to grow under aerobic conditions at 37 °C. L. bulgaricus (10% (v/v)) was inoculated into MRS broth (Criterion™, Hardy Diagnostics, Santa Maria, CA) supplemented with 0.2% (wt/v) sodium thioglycolate (Acros Organics, Fair Lawn, NJ, USA) (an oxygen scavenger to achieve microaerophilic conditions) and 0.3% (wt/v) oxgall bile salt to evaluate its ability to grow under anaerobic conditions at 43 °C. Samples of each culture were taken hourly for 8 h and plated.