Protocol development using an electronic nose for differentiating E. coli strains

The presence of Escherichia coli (E. coli) O157:H7 in the food industry continues to be a problem in America. The pathogenic bacteria, commonly associated with beef products, are the cause of numerous human health concerns. On the other hand, the nontoxic E. coli is present in the intestinal tracts of animals and humans and helps in digestion. Thus, the long-term research objective is to differentiate quickly the pathogen E. coli O157:H7 from the nontoxic strains of E. coli in the farm-to-fork industry chain before the infected food reaches the consumer. This paper describes a constructed gas-sensor electronic-nose system that detects the released gases (amines and alcohol compounds) occurring during the growth of the bacteria cultured in two types of media, namely nutrient broth and brain heart infusion (BHI) broth. The output is a gas signature for each bacterial sample. Eight different E. coli samples were used in testing; four O157:H7 and four non-O157:H7 isolates. Different concentrations of bacteria were used in the study, ranging from 10² to 10⁷ colony-forming units per milliliter. The results of the research showed that E. coli O157:H7 had a distinctly different gas signature than that of the non-O157:H7 bacteria when grown in nutrient broth. Bacteria grown in BHI broth did not have differentiating results. The initiation of gas increase in the bacteria correlated directly with the initial cell concentration of the sample. The initial increase of gas released by the bacteria occurred during the exponential phase of bacterial growth. The electronic nose device was able to differentiate the gas signatures of non-O157:H7 E. coli and O157:H7 E. coli isolates grown in nutrient broth with excellent reproducibility. Potential applications include food and environmental safety from farm to fork.