Is bloody diarrhea a sign of e.Coli infestation?

Sometimes. Bloody diarrhea can been seen with toxic strains of e.Coli like the strain e coli: 0157:h7 of which there is an outbreak in germany. Bloody diarrhea can also be a sign of ulcerative colitis or other invasive bacteria like salmonella, shigella, campylobacter.
Possibly. Agree with dr. Crespin. Bottom line, however, is that if you see blood in your stool or black tar-like stool, you should immediately consult with your doctor and let him or her determine the cause of the bleeding.