Investigations on the generation time of selected gramnegative bacteria species

The purpose of the investigations was to determine the growth behaviour of different strains of Escherichia (E.) coli, Klebsiella (K.) pneumoniae, K. oxytoca, Enterobacter spp. and Pseudomonas (P.) fluorescens. Stepwise the generation times in the range from the temperature optimum to the minimal growth temperature were recorded, A total of 38 different strains (8 E. coli, 10 K. pneumoniae, 6 K. oxytoca, 6 Enterobacter spp., 8 P. fluorescens) were investigated. Impedance measurement basing on the RABIT-System (Don Whitley Scientific Limited, UK) in Whitley Impedance Broth was used to determine the generation times, At 37 degrees C the average generation time of Enterobacteriaceae was between 20 and 24 min. In the P. fluorescens strains the generation time was 52 min at 30 degrees C. In the range of low temperatures significant differences within the Enterobacteriaceae were observed (10 degrees C: E. coli (x) over bar = 358 min, K. pneumoniae (x) over bar = 564 min, K. oxytoca (x) over bar = 232 min, Enterobacter spp. (x) over bar = 249 min). At 10 degrees C the generation time of P. fluorescens was 200 min. Within the Enterobacteriaceae the minimal growth temperatures differed (E. coli 6 degrees C, K. pneumoniae 8 degrees C, K. oxytoco 4 degrees C, Enterobacter spp. 4 degrees C). Only P fluorescens grew at 0 degrees C. In all strains the 95%-confidence interval increased with decreasing temperature. Marked correlative relations between temperature and generation time were found (correlation coefficients between r = -0.863 and r = -0.937, p < 0.001). The data yield best to linear regression relationships. The results extend the knowledge about the growth rate in correlation to the storage temperature of the investigated bacteria.