When E. coli is the topic, people often associate it with diarrheal diseases. However, a recent study supported one strain called E. coli Nissle that could protect people from its harmful counterparts.
The beneficial strain of E. coli was unveiled by scientists at the University of Cincinnati, a public research university in the US. Their findings showed that the Nissle strain could protect the human gut from pathogenic strains of E. coli. Using stem cell-derived cultures, they were able to observe how this friendly strain prevented the invasion of harmful strains. It appeared that Nissle protected the intestinal tissues, which harmful E. coli would normally destroy. They published their findings in the journal mBio.
The Facts on E. coli
Escherichia coli or E. coli is a bacterial species commonly found in the environment, foods, and inside the human body, specifically in the intestines. There are multiple confirmed strains of E. coli that highlighted its diversity in the bacteria world. But the majority of these strains are not friendly to the human body. Most of these can make people sick by causing digestive distress. If these strains reach organs outside the digestive system, they can induce respiratory diseases including pneumonia and urinary tract infections.
According to the US Centers for Disease Control and Prevention (CDC), a federal agency, there are three notable pathogenic strains of E. coli. These are the Shiga toxin-producing E. coli (STEC), enterotoxigenic E. coli (ETEC), and diarrheagenic E. coli. While each can be characterized differently, the illnesses these strains can cause may lead to serious complications and untimely death. STEC is known to produce a bacterial toxin called Shiga to destroy human cells. The invasion can cause symptoms, such as severe stomach cramps and bloody diarrhea. Though, some cases of STEC exhibit mild symptoms.
ETEC, on the other hand, is a widely recognized causative agent of traveler's diarrhea and diarrheal diseases in low-income nations. Symptoms associated with ETEC include stomach cramps, watery diarrhea, fever, nausea, vomiting, appetite lose, muscle aches, and headaches. The majority of people with ETEC virtually recover as long as dehydration is prevented. Diarrheagenic E. coli is a strain normally found in the human intestine. This strain does not cause infection in its normal state, but if the opportunity presents itself, it can become pathogenic.
The Friendly E. coli That Protects the Human Gut
In the recent study at the University of Cincinnati, scientists determined one strain of E. coli friendly to the human gut. Instead of destroying the human intestinal tissues (HIO), the strain would protect it from its harmful cousins. Its protective benefit was observed in a series of experiments using stem cell-derived human intestinal organoid tissues. Based on their findings, the Nissle strain appeared to be beneficial in the human gut. Though, they were unable to determine if E. coli Nissle could become pathogenic if an opportunity arises.
"Nissle did not kill pathogenic E. coli, but rather ramps up your intestinal responses and prepares you for possible pathogens attacking the intestine. We don't know how it does this, but our study confirms its effectiveness in human cells. Our hope is to figure out how this is happening," said Dr. Alison Weiss, an author of the study and professor in the Department of Molecule Genetics at Cincinnati.
In the study, the team utilized three different strains of E. coli to find out how Nissle functions. The strains were the Shiga toxin-producing enterohemorrhagic E. coli (EHEC) 0157:H7 strain, uropathogenic E. coli (UPEC) CFT073 strain, which causes various urinary tract infections, and the Nissle strain. Antibiotic resistance markers were introduced to identify the strains in mixed cultures. The markers were kanamycin resistance for Nissle, gentamicin resistance for UPEC, and streptomycin resistance for EHEC.
Scientists exposed one crucial difference between good and bad E. coli strains. All E. coli strains could collect genes from the environment and other pathogens. These genes could modify the characteristics of the strains and trigger an evolution – one way to develop antimicrobial resistance. But pathogenic genes tend to feature lots of extra genes capable of harmful human cells. Good E. coli strains have been stripped down of those genes, which prevented them from causing harm.
According to their experiments, the Nissle strain caused no harm to the HIOs after being introduced, compared to the other strains that destroyed the epithelial layer. When the good strain was introduced first, it shielded the HIOs from the malevolent attempts of the other strains. That represents its beneficial role in the human gut.
Closer inspection of the interactions between strains showed something interesting. Nissle indirectly fought the EHEC and UPEC strains. The good E. coli caused no harm to its evil cousins, but enhanced the intestinal responses against invaders. The signal from Nissle helped the human cells to prepare ahead of the bacterial invasion. Thus, the harmful E. coli strains were met with resistance that ultimately resulted in their defeat.
According to the September 2016 report of the CDC, approximately 265,000 infections of STEC occur each year in the US alone. The STEC 0157 strain is accounted for 36% of all STEC infections in the country. Every year, STEC infections lead to about 3,600 hospitalizations and 30 deaths in the US. Among those who got infected by STEC 0157 strain, 5% to 10% of patients develop a life-threatening complication called hemolytic uremic syndrome (HUS), a type of kidney failure. The onset of recovery from STEC infection is between five and seven days, faster than the two weeks' usual time to confirm if a person with STEC is a part of an outbreak.
Scientists are hoping they can learn more insights into the Nissle strain. Additional information may show them the capabilities of the strain that can be used to develop a treatment for E. coli infections. Despite the availability of antibiotics, E. coli infections in the gut are not treated by these medications. Also, children treated with antibiotics for E. coli have a higher chance to develop HUS.