Alternatively, adaptation has been used to describe an increase in resistance, following a prior exposure to low levels of stress. For example, the elevated heat resistance of yeast following development of a “heat-shock response”, when cells are first warmed to a sub-lethal temperature, enables cells to survive an otherwise lethal heat shock (Ellis and Hemmingsen, 1989; Steels et al., 1994). Other studies have shown that bacteria suddenly exposed to acidic pH will rapidly die,
whereas cultures acclimatised to mildly acidic conditions express an acid tolerance response (ATR) and subsequently survive better at low pH (Baik et al., 1996; Huhtanen, 1975).