Vmax has a low-level natural resistance to kanamycin but is more susceptible to other antibiotics. When selecting on Kan plates, Vmax with KanR will simply grow faster than Vmax without KanR. Larger colonies=KanR. Other antibiotics select against Vmax but must have a dosage change compared to E. coli.

The stability of susceptibility patterns allowed the antibiograms to be used as aids in the preliminary differentiation of these organisms.