Effect of growth phase, type of acid and medium on acid tolerance of Morganella morganii at different pHs

The ability of bacteria to tolerate low pH is a very important trait to survive in a variety of environments. In the literature، there is a lot of information about the acid tolerance of different bacteria. However، little is known about the acid tolerance of Morganella morganii، the most prolific histamine former in fish and seafood products. Therefore، in the present study، the effect of growth phase، type of acid and medium on the acid tolerance of M. morganii at different pHs were evaluated. To achieve this purpose، cells of M. morganii in exponential or stationary growth phases were exposed to low pHs (3، 4 and 5) adjusted by adding hydrochloric، acetic، lactic، citric or tartaric acids into TSB or PBS for one hour. Survival percentage was obtained by dividing the surviving population by the initial population. In general، results of the present study showed a high acid tolerance of M. morganii. For all the acids tested، the lower the pH of the mediums used، the lower the survival percentage observed. Cells of M. morganii in the stationary phase were more resistant to acidic conditions tested and no significant difference was observed (p<0. 05) in the acid tolerance of M. morganii in TSB and PBS at different pHs. In addition، acetic acid and lactic acid showed more antimicrobial effect on both the stationary and exponential phase cells than the other acids use.