Acid sensitivity as affected by physico-chemical stresses in Aeromonas hydrophila.

This work focuses mainly on the effect of NaCl along with other mono and divalent anions and cations at pH 4 on survival and virulence properties of Aeromonas hydrophila. To find the optimum stress condition, effects of several other physical factors on NaCl induction were also assayed. A. hydrophila collected from International Center for Diarrheal Disease Research, Bangladesh (ICDDR,B) was found to be more sensitive to pH 4.0 when grown in media containing 200 mM or more salt. Induction of acid sensitivity was rapidly gained in NaCl-supplemented broth at 37 C. There was only slight sensitization after 5 min, but a marked effect was observed within 30 min. Uninduced A. hydrophila gave an average of 40% survival after exposure to pH 4.0 for 5 min. However, NaCl-induced cells of this organism reduced the survival to a great extent having an average of 0.06%. Either increase in salt concentration (100 mM through 400 mM) or decrease (50 mM) resulted in decrease in percent survival when exposed to gradually increased concentrations of salt. The most effective dose for induction was 400 mM NaCl salt. NaCl-induction was found to be more pronounced in log-phase organisms. All other monovalent and divalent anions and cations tested were almost as effective as NaCl except KCl.