Determination of the growth stages of Lactobacillus paracasei subsp. paracasei M3 from Bulgarian yellow cheese by electroconductivity.

The growth curve and the bacteriocin production by Lactobacillus paracasei subsp. paracasei M3-a strain isolated from Bulgarian yellow cheese, was studied using electroconductivity measurements in the culture medium (MRS). The bacteriocin produced by this bacterium inhibits strains belonging to the Candida species as well as Bacillus subtilis ATCC 6633. The use of the direct impedance technique coupled with statistical treatment of the results for the strain's growth curve allowed the detection of the growth phase-related bacteriocin production. Definition of the average particle size and aggregation estimations for the cells of the bacteriocin-producing strain was also possible. The comparison of results of impedance measurements with results obtained by classic microbiological methods and microscopic observations confirms the good correlation between these methods. In addition, the advantages of an impedance method such as rapidity, simplicity and higher sensitivity are highlighted.