Purpose: The growth of Escherichia coli O157:H7 in brain-heart infusion broth (BHI), buffered peptone water (BPW), BPW with vancomycin (BPW+V) and BPW with vancomycin, cefixme and cefsulodin (BPW+VCC) was compared at different temperatures.
Methods: An overnight culture of E. coliO157:H7 in tryptic soy broth was diluted to 3 log CFU/ml in each broth. Four hundred microliters were loaded into each well of a Bioscreen C Honeycomb Plate, with eight inoculated wells and two negative controls for each medium. Plates were incubated in the Bioscreen C at 30, 35 or 41°C for 10-15 hours, with optical density (OD) readings every 15 minutes. Three trials were performed at each temperature and the resulting growth curves were fitted to the Gompertz equation using DMFit.
Results: At 30°C, the growth rates in BHI, BPW, BPW+V and BPW+VCC were 0.291 ± 0.008, 0.051±0.005, 0.046 ± 0.002 and 0.037 ± 0.007 hr-1, respectively. At 35°C, these growth rates were 0.349 ± 0.004, 0.057 ± 0.002, 0.053 ± 0.002 and 0.049 ± 0.001 hr-1. Compared to BHI, only small increases in OD were observed in the BPW variations at the lower temperatures. At 41°C, the OD did not increase in the BPW-based enrichments, even when incubation was extended to 24 hours. The growth rate in BHI at 41°C was 0.326 ± 0.015 hr-1.
Significance: Increased temperatures and antibiotics are commonly used during enrichment for E. coli O157:H7. However, no growth was observed in BPW, BPW+V or BPW+VCC at 41°C. These conditions do not appear to be sufficient for the enrichment of this organism. Future experiments with the Bioscreen C will assess the growth of other strains and microorganisms in a variety of enrichment media.