Bacterial DNA was extracted from 1 mL of overnight cultures using Chelex 100 Resin (BioRad, Hercules, CA) and used as the template for the PCR detection of genes listed in Table 2 , as described previously [8] [9] [10] [11] [12] [13] 18] . The primers used to amplify the genes sspH1, sspH2, ssaQ, sopB, siiD, stfE, safC, csgA, ipfD, bcfC, stbD, and fimA were designed using the Primer3 software (version 0.4.0; http:// frodo.wi.mit.edu/), and PCR was performed in a final volume of 25 μL containing HotStar Taq Master Mix (Qiagen, Valencia, CA) 1×, 0.4 μM each primer and 1 μL of extracted DNA. The thermal profile included an initial denaturation step at 95°C for 15 min, followed by 35 cycles at 95°C for 30 s, 58°C for 30 s, and 72°C for 1 min, and a final extension step at 72°C for 5 min. Amplification products were visualized under ultraviolet (UV) light after electrophoresis on 3% agarose gels and staining with SYBRsafe (Invitrogen, Carlsbad, CA).