In those examples, it's the host, not the lab, that is the risk. We all carry those organisms to some extent on our bodies, and it's when the wrong set of circumstances occur that it's allowed to cause disease, whether it's from taking an antibiotic and getting C. difficile colitis, or whether it's from a urinary tract infection due to E. coli. Those originate in the host, not in the laboratory.
On March 10th, 2009. See this statement in context.