Figure 6.

Detection of bacteria from bacterium-contaminated cherry tomatoes. (A) Photograph of the cotton swabs obtained after sampling bacteria from the cherry tomatoes smeared with PBS only, and ~3.4 × 10⁷–3.4 × 10⁴ E. coli O157:H7 cells (left to right), followed by dipping into a reagent (50 µL) containing H₂O₂ (~11.2 mM) and TMB (1.25 mM) at pH 3. (B) Photograph of the as-prepared tomato that was sampled by a cotton swab. The photograph inset on the right-hand side shows the three swabs obtained after sampling bacteria from the surface of three individual tomatoes smeared with ~10⁶ cells of E. coli O157:H7, followed by immersion in a reagent droplet (50 µL) containing H₂O₂ and TMB at pH 3. (C) Photograph of the samples obtained after collecting bacteria from the cherry tomatoes smeared with ~3.4 × 10⁴–~3 E. coli O157:H7 cells (left to right), followed by incubation in a growth broth (0.4 mL) for 4 h and then reacted with the reagent (0.2 mL) containing H₂O₂ (~11.2 mM) and TMB (1.25 mM) at pH 3, and the addition of sulfuric acid (2 M, 2 µL). (D) The corresponding UV–Vis absorption spectra of the samples obtained in (C).