Evaluation of potential sensitization of Morganella morganii to acidic conditions by Ethanol and EDTA

The ability of bacteria to tolerate low pH is a very important trait to survive in a variety of environments. Morganella morganii، the most prolific histamine former in fish and seafood products، has the ability to tolerate low pH and survive in acidic environments. In the present study، the ability of EDTA and ethanol to sensitize M. morganii to low pH and organic acids was assessed. To achieve this purpose، cells of M. morgani in exponential or stationary growth phases were exposed to pH=5، adjusted by adding hydrochloric، acetic، lactic، citric or tartaric acids into TSB، in the presence of 5 % ethanol and/or 7. 5 mM EDTA، for one hour. Survival percentage was obtained by dividing the surviving population by the initial population. According to the results of the present study، 5 % ethanol made both the exponential and stationary phase cells of M. morganii more sensitive to acidic environments tested (p<0. 05). The same results were observed for 7. 5 mM EDTA. Combination of 5 % ethanol and 7. 5 mM EDTA in acidic environments showed more pronounced effects on the acid tolerance of M. morganii (p<0. 05)، while in the presence of this combination the lowest survival percentages of exponential and stationary phase cells of the bacterium were observed. Thus، ethanol and EDTA، individually or combined، can enhance the rate of inactivation of M. morganii during exposure to low pH and organic acids. Furthermore، in the present study، exponential phase cells of M. morganii were more susceptible to acidic conditions than the stationary phase cells (p<0. 05).