C. difficile isolates

In total, 394 C. difficile isolates were collected from CDI patients on a purely random basis without selection between January 2015 and March 2016. Isolates from Perth, Australia (n = 31); Sydney, Australia (n = 54); Busan, South Korea (n = 50); Singapore (n = 29); Fukuoka, Japan (n = 70); and Hong Kong, China (n = 50) were sent to our laboratory in transport medium for anaerobes. A total of 60 isolates were from New York, USA for the purpose of comparison. Fifty isolates were cultured from fecal samples collected from CDI patients in Hangzhou, China, as previous assays reported [16]. All isolates were recovered on cefoxitin-cycloserine fructose agar plates (Oxoid, Basingstoke, United Kingdom) incubated for 48 h at 37°C in an anaerobic chamber with GENbag Anaer (bioMérieux, Marcy l’Etoile, France). Six control strains, including ATCC 43255 (RT087), ATCC BAA-1870 (ST1, RT027), and ATCC BAA-1801(RT010) were obtained from the American Type Culture Collection (ATCC; Manassas, VA, USA).