Estimation of lactic acid bacterial cell number by DNA quantification

Area of Science:

• Microbiology
• Food Science
• Quality Control

Background:

• Lactic acid bacteria (LAB) are vital in fermented foods, beverages, medicines, and supplements.
• Accurate enumeration of LAB is essential for product quality and efficacy, as their benefits correlate with cell numbers.
• Standard colony-counting methods are inadequate for products containing predominantly dead LAB.

Purpose of the Study:

• To develop a simple and accurate method for estimating total lactic acid bacteria cell numbers in products.
• To assess the feasibility of using DNA quantification to determine LAB cell counts, especially in the presence of dead bacteria.

Main Methods:

• Investigated the viability of Enterococcus faecalis and Lactobacillus paraplantarum under heat treatment and long-term culture conditions.
• Quantified DNA extracted from both live and dead LAB cells subjected to different treatments.
• Compared DNA quantification results with standard viability assessments.

Main Results:

• Heat treatment significantly reduced viable Enterococcus faecalis, but DNA content remained substantial.
• Long-term culture reduced viable Lactobacillus paraplantarum, yet DNA extraction yielded high recovery rates.
• DNA quantification effectively estimated the total cell number of LAB, even after cell death induced by heat or extended culture.

Conclusions:

• DNA quantification is a viable alternative to colony counting for estimating total lactic acid bacteria cell numbers in products.
• This method is particularly useful for quality control of products containing non-viable LAB.
• The findings support the use of DNA-based methods for accurate assessment of LAB in various matrices.