Kinetics of interactions of lactic acid, pH and atmosphere on the growth and survival of Yersinia enterocolitica IP 383 O:9 at 4 degrees C.

The influence of different lactic acid concentrations (0.1, 0.3, 0.5, 0.7, 0.9, 1.1% v/v), within pH range of 3.9 to 5.8 on the aerobic and anaerobic growth and survival kinetics of the virulent strain of Y. enterocolitica IP 383 O:9, was determined in Tryptone Soy Broth at 4 degrees C. Growth and survival data were analyzed and fitted by a modification of the Whiting and Cygnarowicz-Provost model, using the Minpack software library. Initial generation times, initial specific growth rates, lag times and death rates were subsequently calculated from the model parameters. The stability of the virulence plasmid in growing and surviving cells was examined using crystal violet binding, low-calcium response and congo red uptake. The results demonstrate the dependancy of the growth and survival kinetics on the interaction between the three variables. The effect of lactic acid on Y. enterocolitica is greater under anaerobic than aerobic conditions. Nevertheless, the organism was found to be more tolerant of low pH conditions under anaerobic atmosphere than under an aerobic atmosphere in the absence of lactic acid. The interaction between the variables did not lead to loss of the virulence plasmid in growing or non-growing cells.