EFFECTS OF TEMPERATURE, MEDIUM COMPOSITION, PH, SALT AND DISSOLVED-OXYGEN ON HEMOLYSIN AND CYTOTOXIN PRODUCTION BY AEROMONAS-HYDROPHILA ISOLATED FROM OYSTER

The effects of temperature, medium composition, pH, salt content and d issolved oxygen (DO) on the production of haemolysin and cytotoxin by one strain of Aeromonas hydrophila isolated from oyster were investiga ted. Four media were tested: brain heart infusion broth (BHIB), casami no acid-yeast extract broth (CAYEB), nutrient broth (NB), and tryptica se soy broth (TSB). BHIB was the best for toxin production even though the growth rates for Aeromonas hydrophila in all of these media were quite similar. Aeromonas hydrophila could produce haemolysin and cytot oxin at 37, 28 and 5 degrees C; however, the toxins were produced fast er and were more stable at 28 degrees C than at 37 degrees C. Although Aeromonas hydrophila itself is tolerant to 5% (w/v) salt in BHIB and a pH range of pH 5.5 to 10.0, the production of haemolysin and cytotox in was apparently decreased in the presence of 1-5% (w/v) NaCl or when the pH of the medium was greater or less than 7.2. The DO values in t he culture medium during the stationary growth phase also seemed to af fect toxin production; greater quantities of toxins were produced when the DO values were higher. (C) 1997 Elsevier Science B.V.