9/18/2016 pH and Foodborne Pathogens ·Lower the pH pH Regulates Gene Expression ·Exernal pH regulates the less energy producing toxins Foods with lower pH require less processing Proton transport Foodborne pathogens Amino acid degradation Stress response ·persist or slowly die Virulence Spoilage microbes can grow in acid products Neutral pH is maintained to prevent th proteins from denaturing ●800000689 Bacteria Sense pH Maintaining pH Homeostatic response Hydroxyl ions cannot pass through the membrane but Accumulation of anions or protons do,wihch affects the pH of the cytoplasm protons in the cytoplasm .Gram-negative enteric bacteria maintain a pH of 7.8 Change in transmembrane With a shift in acidity,K'/H'antiporter pumps in proton gradient K'neutralizing the pH Altered protein conformation With a shift to alkaline,the Na'/H antiporter due to protonation and acidifies the cytoplasm deprotonation of amino acids .Proton antiporters are good for transient shifts in pH .Prolonged exposures require metabolic changes 139/18/2016 13 pH and Foodborne Pathogens • Lower the pH - the more energy the cell needs to maintain a neutral intracellular pH - the less energy producing toxins • Foods with lower pH require less processing • Foodborne pathogens - grow optimally at neutral pH - do not grow below pH 4.4 or above pH 8 - p y ersist or slowl y die • Spoilage microbes can grow in acid products 49 pH Regulates Gene Expression • Exernal pH regulates - Proton transport - Amino acid degradation - Stress response - Virulence • Neutral pH is maintained to prevent proteins from denaturing 50 Bacteria Sense pH • Accumulation of anions or prot i th t l tons i n th e cy toplasm • Change in transmembrane proton gradient • Altered protein conformation due to protonation and deprotonation of amino acids 51 Maintaining pH Homeostatic response • Hydroxyl ions cannot pass through the membrane but protons do, wihch affects the pH of the cytoplasm • Gram-negative enteric bacteria maintain a pH of 7.8 - With a shift in acidity, K+/H+ antiporter pumps in K+ neutralizing the pH - With a shift to alkaline, the Na+/H+ antiporter acidifies the cytoplasm • Proton antiporters are good for transient shifts in pH • Prolonged exposures require metabolic changes 52