Figure 7.

Detection of bacteria from door handles. (A) Photograph of the cotton swabs obtained after sampling bacteria from door handles smeared with the bacterial samples, including E. coli J96 (2.7 × 10⁵ cells), the mixture of E. coli J96 (~2.7 × 10⁵ cells) and S. aureus (~8.5 × 10⁷ cells), and two S. aureus samples with different cell numbers (~8.5 × 10⁵ cells (S. aureus 1) and ~8.5 × 10⁷ cells (S. aureus 2)), 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 cotton swabs from Panel A, obtained after further reaction with a reagent containing H₂O₂ (180 mM, 0.1 mL) at pH 3. (C) Photograph of the swabs used to collect bacteria from the door handles from the restroom, obtained after reaction with the reagent (50 µL) containing TMB (1.25 mM) and H₂O₂ (~11.2 mM). (D) Photograph of the cotton swabs from Panel C, obtained after further reaction with H₂O₂ (180 mM, 0.1 mL) at pH 3.