Abstract
An innovative and low-cost method is proposed for the detection and discrimination of indole-positive pathogen bacteria. The method allows the non-invasive detection of gaseous indole, released by bacteria, with nanoporous colorimetric sensors. The innovation comes from the use of nanoporous matrices doped with 4-(dimethylamino)-cinnamaldehyde, which act as sponges to trap and concentrate the targeted analyte and turn from transparent to dark green, long before the colonies get visible with naked eyes. With such sensors, it was possible to discriminate E. coli from H. alvei, two indole-positive and negative bacteria after seven hours of incubation.
Highlights
Microbial contamination is an important problem in medicine, food, the pharmaceutical industry, and in biotechnology
Indole is a widespread metabolite of a large variety of both Gram-positive and Gram-negative bacteria: to date, more than 85 species including many pathogens [14,15,16,17], the most commonly known being Escherichia coli
No significant amount of indole was detected at t = 0 in cultures of E. coli, nor throughout the whole experiment in cultures of H. alvei, and in non-inoculated LB samples. These results demonstrate that H. alvei bacteria do not show any tryptophanase activity and that LB Lennox does not contain any significant amount of indole
Summary
Microbial contamination is an important problem in medicine, food, the pharmaceutical industry, and in biotechnology. Optical spectroscopic methods including fluorescence, Raman, IR, that give information about the chemical composition of bacteria, have been shown to discriminate between bacteria down to the strain level [2,3] The use of such methods, is limited by the complexity of the associated instrumentation and protocols, and the need to show a good correlation of their results with those of the robust and low cost phenotypic reference methods. A large number of VOC including alkanes, alkenes, alcohols, ketones, aldehydes, thiols or amines were identified and quantified so that a ―VOC profile‖ could be in some cases correlated with bacterial identification Such methods provide unprecedented sensitivity and specificity for detection and identification of VOCs in complex mixtures, the complexity and cost of the instrumentation used still largely precludes their use in the field. The resulting sensor could be used to measure the concentration of bacterial indole, in chemically complex environment, either in the liquid or gas phases
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