The group of bacteria called Enterobacteriaceae, including Klebsiella pneumoniae, Shigella, E. coli and others, is present at low levels as part of a healthy human gut microbiome. But at high levels—caused, for example, by increased inflammation in the body, or by eating contaminated food—these bugs can cause illness and disease. In extreme cases, too much Enterobacteriaceae in the gut can be life-threatening.
Source: Medical Xpress