In the case file the organism responsible for the patient's death is a normal member of the human microbiota. how do you explain it cause the death of the patient

Even if a microorganism is a part of the normal microbiota of a human being, it may cause the death of the person. For example, say E. coli, it resides in intestines and is harmful. But, if its number increases way too large, it may cause infection (Colitis) and even death. So, even the normal microflora needs to be present in the controlled quantities, inside the body.