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<i>Escherichia coli</i> O157:H7 and <i>Staphylococcus aureus</i> are common pathogens. Gram-negative bacteria, such as <i>E. coli</i>, contain high concentrations of endogenous peroxidases, whereas Gram-positive bacteria, such as <i>S. aureus</i>, possess abundant endogenous catalases. Colorless 3,5,3′,5′-tetramethyl benzidine (TMB) changes to blue oxidized TMB in the presence of <i>E. coli</i> and a low concentration of H₂O₂ (e.g., ~11 mM) at pH of 3. Moreover, visible air bubbles containing oxygen are generated after <i>S. aureus</i> reacts with H₂O₂ at a high concentration (e.g., 180 mM) at pH of 3. A novel method for rapidly detecting the presence of bacteria on the surfaces of samples, on the basis of these two endogenous enzymatic reactions, was explored. Briefly, a cotton swab was used for collecting bacteria from the surfaces of samples, such as tomatoes and door handles, then two-step endogenous enzymatic reactions were carried out. In the first step, a cotton swab containing bacteria was immersed in a reagent comprising H₂O₂ (11.2 mM) and TMB for 25 min. In the second step, the swab was dipped further in H₂O₂ (180 mM) at pH 3 for 5 min. Results showed that the presence of Gram-negative bacteria, such as <i>E. coli</i> with a cell number of ≥ ~10⁵, and Gram-positive bacteria, such as <i>S. aureus</i> with a cell number of ≥ ~10⁶, can be visually confirmed according to the appearance of the blue color in the swab and the formation of air bubbles in the reagent solution, respectively, within ~30 min. To improve visual sensitivity, we dipped the swab carrying the bacteria in a vial containing a growth broth, incubated it for ~4 h, and carried out the two-stage reaction steps. Results showed that bluish swabs resulting from the presence of <i>E. coli</i> O157: H7 with initial cell numbers of ≥ ~34 were obtained, whereas air bubbles were visible in the samples containing <i>S. aureus</i> with initial cell numbers of ≥ ~8.5 × 10³.