Chapter Acid tolerance
Acid tolerance response is a complex defense system that can minimize the lethal effects of extreme low pH (pH 3) and also the effect of weak organic acids (Baik et al., 1996). Survival of organic and inorganic challenges differs among microorganisms with regard to physiological requirements. One example can be seen in Listeria monocytogenes where δB may mediate protection against both organic and inorganic acid stresses, but through different mechanisms (Ferreira et al., 2003). Also, Salmonella enterica sv. typhimurium cells that have been exposed to acid shock, show varying sensitivities to organic acids (Baik et al., 1996; Tetteh and Beuchat, 2003). Two systems exist in S. typhimurium that provide redundant protection against inorganic acid stress. These are (1) RpoS dependent, and (2) PhoPQ dependent, where PhoP is an acid-shock protein (Bearson, Wilson, and Foster, 1998).