Model trials to characterise the influence of temperature and pH value on the generation times of selected Enterobacteriaceae strains

Generation times were impedimetrically determined by using different strain s of different Enterobacteriaceae species and genera. The trials were carri ed out with 30 strains, representing 10 genera respectively species, in rel ation to temperatures from 7 degrees C to 40 degrees C and pH-values betwee n 5.0 and 7.3. Under favourable milieu conditions the generation times were almost homogenous, except for the Yersinia spp. strains which showed longe r generation intervals. The shortest average generation time with 21 min wa s ascertained at 37 degrees C and at pH-value of 6.5. Temperatures of 20 de grees C and less extended seriously the generation times, acid pH-values le ss than or equal to 5.5 had a synergistic effect on this. On contrary the i nfluence of the medium-pH-value was more marginal at incubation temperature s above 20 degrees C. Under unfavourable milieu conditions, the mean variat ion of results increased and therefore generation times differed between th e different strains.