Intracellular pH Determination for the Study of Acid Tolerance of Lactic Acid Bacteria
It is important to assess acid tolerance in lactic acid bacteria, particularly for probiotics, although it involves multiple mechanisms. Measuring the difference between intracellular and extracellular pH (ΔpH) using the fluorescent probe CFDA-SE is particularly effective for such assessments because it gives direct information on the level of tolerance in the extracellular acidic pH range from 7 to 2.5. It also enables acid adaptation to be induced and observed by slowly introducing HCl into the medium and decreasing the extracellular pH. The difference of acid tolerance between anaerobic and aerobic conditions in lactic acid bacteria can also be evaluated by measuring ΔpH.
Key wordsΔpH Acid tolerance Acid adaptation Intracellular pH Anaerobic condition Fluorescent probe CFDA-SE
The authors would like to thank Professor Dr. A. Yokota in Hokkaido University for teaching the measurement of intracellular pH and Enago (www.enago.jp) for the English language review.