Is 100,000ml of escherichia coli dangerous?

Assuming that's the result of a urine culture, it means there is an active E. coli urinary tract infection. UTIs can range from no symptoms (which may or may not need treatment) to extremely severe, requiring hospitalization and IV antibiotics. It depends on symptoms, exam findings, and perhaps other tests (blood count etc) in the infected person. Follow your doctor's advice. Good luck.