Impedimetric method for physiologically characterisation of fungi

Fungi are playing an important role in the food and pharmaceutical industry today, both as starter cultures, fermentation organisms, and as contaminants. Characterisation of fungal growth is normally time consuming as it includes measurements and study on a wide range of media at different temperatures, pH, water activity and atmosphere composition.

Nevertheless is it important information in ecophysiological studies, where the growth potential by fungi are related to composition and storage of food. It is therefore of great interest to device a rapid method for characterisation of fungi.The objective was to determine the growth phases of various fungi using an impedimetric method and compare this with traditional methods using agar plates, in order to determine if this rapid method can replace the traditional method.The method is based on impedimetric assessment of growth on the Bactometer 128-3 (bioMèrieux, UK).

Experiments were carried out as a factorial design, studying the effect of temperature, pH and sodium chloride on growth. All data analysis were performed using Partial Least Square analysis (PLS).Good correlation between growth characterisation (growth rate, lag phase and generation time) on the Bactometer and agar plates were obtained.

The two methods present two phases of the growth of fungi; exponential growth observed after growth on the Bactometer (first 2-3 days) and a linear growth observed after growth on agar plates (after 2-3 days). It was also found that growth depends on incubating temperature and media composition. This result shows that impedimetri may be used as a rapid alternative to traditional physiological characterisation of fungi.