Other protective acid stress defense systems include chan in cell membrane composition. Membrane acid content was a major factor in the acid resistance of E.coil (Brown and others 1997; Chang and Cronan 1999). In E.coil correlation between induction of acid resistance and incre levels of phospholipids containing membrane-stabilizing cyclopropane fatty acids has been reported (Brown and others 1997)Jordan and others 1999). In addition, homeostatic systems for internal pH (Foster and Hall 1991; DeBiase and others 1999) pathways for repair protection of essential cellular compone Raja and others 1991; Cheville and others 1996) have been attributed to acid stress defense mechanisms.