Bacterial colonies can develop chiral morphology in which the colony c
onsists of twisted branches, all with the same handedness. Microscopic
observations of the chiral growth are presented. We propose that the
observed (macroscopic) chirality results from the microscopic chiralit
y of the flagella (via handedness in tumbling) together with orientati
on interaction between the bacteria. The above assumptions are tested
using a generalized version of the communicating walkers model.