Rapid Detection of Pathogenic Bacteria by the Naked Eye

Abstract

Escherichia coli O157:H7 and Staphylococcus aureus are common pathogens. Gram-negative bacteria, such as E. coli, contain high concentrations of endogenous peroxidases, whereas Gram-positive bacteria, such as S. aureus, possess abundant endogenous catalases. Colorless 3,5,3′,5′-tetramethyl benzidine (TMB) changes to blue oxidized TMB in the presence of E. coli and a low concentration of H2O2 (e.g., ~11 mM) at pH of 3. Moreover, visible air bubbles containing oxygen are generated after S. aureus 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 E. coli with a cell number of ≥ ~105, and Gram-positive bacteria, such as S. aureus 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 E. coli O157: H7 with initial cell numbers of ≥ ~34 were obtained, whereas air bubbles were visible in the samples containing S. aureus with initial cell numbers of ≥ ~8.5 × 103.

Application of Multispectral Images from Unmanned Aerial Vehicles to Analyze Operations of a Wastewater Treatment Plant

“…The supposition of the influence of biomass variation in compartments on UAV spectral indices was attempted to substantiate with UV-VIS spectra of the phosphorus bacteria Bacillus megaterium, where the absorption maximum occurred at 550 nm [41]. In addition, the validity of the conjecture may have been evidenced by the UV-VIS spectra of other microorganisms for which the absorption maxima were in the red wavelength range [42,43]. These conclusions can be used in the operation stage of the treatment plant and may provide a solution for obtaining data on the performance of the bioreactor in emergency situations.…”

Recent Advances in Optical Sensing for the Detection of Microbial Contaminants

“…In a previous study, E. coli was detected with the naked eye using colorless 3,5,3′,5′ tetramethyl benzidine (TMB). Its color changes to blue from oxidized TMB in E. coli spiked medium [ 48 ]. Covalent binding, electrostatic interactions, and nano-films can be good candidates for stable docking states [ 49 , 50 ].…”

Europium Ion-Based Magnetic-Trapping and Fluorescence-Sensing Method for Detection of Pathogenic Bacteria

“…Many people die or become ill due to infections caused by pathogenic bacteria Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Acinetobacter baumannii, Bacillus cereus, and Pseudomonas aeruginosa are common foodborne pathogens. ,, Generally, these pathogens exist in complex samples . Classical methods with time-consuming overnight culture followed by bioassays are usually employed .…”