MODEL FOR THE ANAEROBIC GROWTH OF AEROMONAS-HYDROPHILA-K144

The combined effects of temperature (5 to 42-degrees-C), NaCl (0.5 to 4.5%), pH (5.3 to 7.3), and NaNO2 (0 to 200-mu-g/ml) on the anaerobic growth of Aeromonas hydrophila K144 were studied in brain heart infusion broth using a modified central composite design. Variable combinations were tested in triplicate anaerobic flasks (nitrogen atmosphere in sealed trypsinizing flasks); viable cell counts were made at intervals during incubation by surface plating on tryptic soy agar. Growth curves were generated using the Gompertz equation in conjunction with a nonlinear regression analysis program. Values for the four Gompertz parameters (A, C, B, and M) were obtained for the variable combinations tested. Using response surface techniques, regressions were performed on Ln (B), Ln (M), Sqrt (B), and Sqrt (1/M); quadratic and cubic equations containing the four variables of temperature, NaCl, pH, and NaNO2 were developed to yield predictive values for the B and M Gompertz values. Goodness of fit evaluation of the models was determined by R2 values. Comparison of predicted and observed values of B and M and evaluation of predicted lag and generation times indicated that the quadratic model gave the best fit. Overall, the variable combinations interacted to affect the generation and lag times. The results indicate that pH, salt level. and nitrite level can be manipulated to decrease the growth of A. hydrophila when combined with low temperature incubation and anaerobic conditions.