E.coli Lac+

Typical biochemical properties of E.coli are:
  • lactose fermentation (red colonies and red coloured agar around colonies on Endo)
  • D-mannitol fermentation (red coloured agar and colonies around mannitol tablet)
  • negative cellobiose fermentation (colorless colonies and agar on Endo around cellobiose tablet)
  • acid from glucose with gas
  • hydrogen sulfide negative
  • about 50% of all strains ferments sucrose

  • General description of testing on Endo agar with biochemical slope is here.

    Other (more or less) necessary tests for identification are:
  • Indole production (positive)
  • Voges-Proskauer test (negative)
  • Simmons citrate (negative)
  • Malonate utilization (negative)
  • Lysin decarboxylase (typically positive)
  • Arginine dihydrolase (typically negative)
  • Ornithine decarboxylase (can be positive or negative; more strains are positive)

  • Compare these lactose positive isolates with lactose delayed E.coli strains.

    Cultivation 24 hours, 37°C in an aerobic atmosphere.