Humans have a love-hate relationship with the species of bacteria known as Escherichia coli. We hear about outbreaks of food-borne illness associated with E. coli, (and those are becoming less frequent) but many are unaware of the other roles E. coli plays. Those roles are outlined in a new report titled "E. coli: Good, Bad & Deadly,” produced by the American Academy of Microbiology.

The authors point out that the vast majority of E. coli strains are not harmful, and some are beneficial in several ways. We carry, for example, populations of E. coli in our digestive systems that aid in digestion and help prevent establishment of harmful microbes. The report notes that the average human gut contains about 90 trillion microbes. With the human body composed of about 10 trillion cells, the microbes in our digestive system outnumber our human cells by nine to one. The entire role of these microbes in human health and nutrition is not fully understood.

E. coli has however, been the subject of intense scientific study. The bacterium was one of the first organisms to have its complete set of genes, or genome, sequenced. Eleven scientific studies using E. coli, dating back to 1958, have earned the Nobel Prize. Studies on the organism have contributed to scientists’ understanding of the genetic code, how viruses reproduce in cells and recombinant DNA or genetic engineering.

The authors also note that scientists and regulators have used harmless strains of E. coli as an indicator of contamination in food and water supplies. Although the E. coli itself is harmless, it generally originates in animal digestive systems and its presence indicates traces of fecal contamination that could involve more dangerous microbes.

That issue of fecal contamination leads to the “bad” and “deadly” aspects of E. coli’s “good, bad & deadly” split personality. The report notes that some E. coli that are harmless when growing in the gut can cause infections if they get into the blood stream, urinary tract infections if they grow in the urethra, or kidney failure if they grow in the kidneys. Several classes of pathogenic E. coli can cause minor or serious illness in humans, including the well-known strain known as O157:H7, along with other Shigatoxin producing E. coli or STEC.

The STEC strains, while relatively rare, are shed in livestock and wildlife manure, potentially contaminating food products. Beef can be contaminated during processing, and vegetables sometimes become contaminated due from manure used as fertilizer or accidental exposure to manure. “Short of avoiding these foods entirely, it is impossible to reduce the risk of foodborne E. coli infection to zero,” the report notes, “although safe food handling practices can reduce the risk substantially.

The dose makes the poison in the case of STEC-related illnesses, the report notes, with higher numbers of E. coli cells in food causing more frequent and more serious illness. This is why the beef industry has focused on a “multiple hurdles” approach using a series of steps to reduce E. coli contamination during beef processing.

Fortunately, the authors note, outbreaks of E. coli-related illness are on the decline, even though news coverage might make consumers think otherwise. Reports from the U.S. Centers for Disease Control and Prevention show a significant decrease in the number of E. coli O157 cases in the last fifteen years.

Better surveillance and detection of outbreaks results in more outbreaks being identified, but the vast majority affect a small number of people, according to the report. Rapid detection and investigation of outbreaks with better public health surveillance, more microbial testing, and increased regulatory authority to recall products when E. coli O157 is detected have contributed to the decrease in the number of cases.