Bioelectroanalytical Detection of Lactic Acid Bacteria

Lactic acid bacteria (LAB) are an industrial important group of organisms that are notable for their inability to respire without growth supplements. Recently described bioelectroanalytical detectors that can specifically detect and enumerate microorganisms depend on a phenomenon known as extracellular electron transport (EET) for effective detection. EET is often described as a type of microbial respiration, which logically excludes LAB from such a detection platform. However, members of the LAB have recently been described as electroactive with the ability to carry out EET, providing a timely impetus to revisit the utility of bioelectroanalytical detectors in LAB detection. Here, we show that an LAB, Enterococcus faecalis, is easily detected bioelectroanalytically using the defined substrate resorufin-beta-d-galactopyranoside. Detection is rapid, ranging from 34 to 235 min for inoculum sizes between 10(7) and 10(4) CFU mL(-1), respectively. We show that, although the signal achieved by Enterococcus faecalis is comparable to systems that rely on the respiratory EET strategies of target bacteria, E. faecalis is not dependent on the electrode for energy, and it is only necessary to capture small amounts of an organism's metabolic energy to, in this case 1.6%, to achieve good detection. The results pave the way for new means of detecting an industrially important group of organisms, particularly in the food industry.

Automated summary

Lactic acid bacteria (LAB) are an industrially important group of organisms. Recently, it has been discovered that LAB have the ability to perform extracellular electron transport (EET), which allows them to be detected using bioelectroanalytical detectors. This study demonstrates that Enterococcus faecalis, a LAB, can be rapidly and accurately detected using bioelectroanalytical methods, providing a new means of detecting industrially important microorganisms.