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Journal of Biological Sciences
Year: 2002  |  Volume: 2  |  Issue: 1  |  Page No.: 53 - 57

Influence of Different Physico-Chemical Stresses on Growth and Survivality of Shigella dysenteriae and Shigella flexneri

Ishrat Sultana, Rahman Md. Mizanur, Shakhawat Hossain Bhuiyan and Md. Majibur Rahman    

Abstract: This study relates to the survivality of Shigella dysenteriae and S. flexneri in acid environment and the effect of salt induction on subsequent sensitivity to acid. After 120 min exposure to acidic environment at pH 3, around 30% survivality of both the Shigella spp. was recorded. The acid tolerance was found to be dependent on the growth phase and the pH of the growth medium. Shigella spp. previously grown in low-salt broth at pH 7.2, produced organisms which were markedly more acid sensitive when subsequently cultured in the same broth supplemented with 200 mM or more salt at 37 °C. However The 0 degree of sensitivity varied with the time of exposure in different salts. Almost no viable cells were recorded after 30 min exposure when treated with 500 mM salt at pH 3. Survivality of salt treated Shigella spp. was also found to be influenced by different water samples. Viable counts could be observed up to 6 days in normal saline, where as, in pond-, tap- and distilled water Shigella spp. were not detected after 96, 72 and 72 h respectively. Shigella spp. treated with 500 mM salt went into non-culturable state but remain viable as was detected by acridine orange staining method. No significant changes of the virulence properties of NaCl treated Shigella spp. was noted.

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