Understanding the Tolerance of Different Strains of Human Pathogenic Bacteria to Acidic Environments

It is known that many bacteria are susceptible to low pH, but it is less clear how the acid nature influences this susceptibility. The objective of this work was to evaluate the susceptibility of selected bacteria to different low pH conditions and to understand if their tolerance is affected by the type of acid (organic vs inorganic) in the media acidification. Strains of different species of human pathogenic bacteria were cultivated at different acidic conditions, using organic or inorganic acids. Overall, we verified that tolerance to acidic conditions is dependent on the type of acid used to acidify the growing medium, organic or inorganic. The strains analysed, although having different tolerance to low pH, were shown to be more susceptible to organic than inorganic acids. This result shows that beyond the pH of the media, the nature of the acid affects bacterial growth. Such a result has consequences in the evaluation of the efficiency of an antibacterial extract, which should take into consideration the differential susceptibility of bacteria to low pHs obtained using organic or inorganic acids.