Growth of 10 strains of VTEC O157, which were isolated from faecal specimens, was evaluated in conventionally recommended enrichment broth media Trypticase soy broth (TSB) and Davis's Minimal Medium (DMM) at different temperatures.
Five strains of VTEC O157 used in the test proliferated well in TSB and reached to 10⁹ CFU/ml at 36°C in 24 hours incubation and to the same population densities at 25°C in 48 hours. Whereas in DMM at 36°C there was no prolifiration in 6 hours, but grew to 10⁶ CFU/ml in 24 hours and 108 CFU/ ml in 48 hours. Three strains of VTEC O157 tested at 25°C grew to 1.52×10⁴ CFU/ml in 24 hours, 1.67×10⁸ CFU/ml in 48 hours and 6.80×10⁸ CFU/ml in 72 hours. No proliferation was observed at 4°C in 72 hours in groth TSB and DMM.
The growth in glucose free DMM was found in 7 out of 10 strains, and 4 out of these 7 strains grew profusely to 10⁵ CFU/ml in 48 hours. One out of 3 strains showed no prolifiration but survived 72 hours postinoculation, decreasing from 179 CFU to 29 CFU in 100μl of medium. The other 2 strains became completely extinct in 48 hours after inoculation with 263 CFU and 2, 420 CFU in 100g1 of medium respectively. However, these 3 strains which showed no growth in glucose free DMM could proliferate in DMM containing 1/10 of the usual glucose concentration, at a rate depending on the concentration.
In conclusion, it is suggested that the finding of increase of VTEC O157 in glucose free DMM would be a useful solution for the food poisoning problem caused by VTEC O157.