Observation of S . Typhimurium LB5010 and the S . Typhimurium Δ stm0551 strain by electron microscopy. Panel A: S. Typhimurium LB5010 obtained following growth under static LB broth conditions at 37°C for 48 h produced type 1 fimbrial appendages (40,000 ×). Panel B: No fimbrial structures were observed on the S. Typhimurium LB5010 grown on LB agar at 37°C for 18 hr (30,000 ×). Panel C: S. Typhimurium Δstm0551 cells obtained from static LB broth condition at 37°C for 48 h produced type 1 fimbrial appendages (15,000 ×) whereas the fimbrial appendages were also observed when these cells were cultured on LB solid agar (panel D) (40,000 ×). Bacterial cells were negatively stained with 2% phosphotungstic acid.