There are many different kinds of Escherichia coli bacteria. Some of them are normal parts of the human gut microbiome; others have been genetically modified for use in the research laboratory, and they are relatively harmless; while other E. coli strains can generate toxins that can harm human cells. Shiga toxin-producing Escherichia coli (STEC) is one of those strains, and it often causes severe diarrheal disease in the young and old around the world.
Now scientists have discovered another toxin generated by some E. coli strains. This toxin, called EspC, is an enzyme that can rip gut cells open, which leads to serious illness and potentially death. The E. coli that generates EspC toxin is known as EPEC. The study has revealed the three-dimensional structure of the toxin, and the work has been reported in Gut Microbes.
"Many strains of E. coli, including EPEC, which is a major cause of diarrheal disease, are becoming increasingly resistant to the antibiotics commonly used to treat these infections," noted co-corresponding study author Professor Begoña Heras of La Trobe University. "This is alarming as 1.3 million children under the age of 5 die each year from diarrheal illnesses due to the associated severe dehydration and loss of essential electrolytes."
But by revealing how this toxin works, researchers may be able to develop better treatments for infections caused by EPEC.
When toxin-generating E. coli bacteria causes a gut infection, it's typically treated with broad-spectrum antibiotics. But these drugs can simply kill wide swaths of both beneficial and harmful microbes in the gut, which can lead to other problems. The researchers stressed that many E. coli strains are also gaining resistance to these broad antibiotics.
"New antibiotics are still being developed, but the pace is extremely slow and when they become available, they're often put in a stewardship and only used when absolutely necessary, as bacteria can develop resistance within just a few years," added co-corresponding study author Dr. Jason Paxman. "This is a huge issue, as most traditional antibiotics do not target specific bacteria, which means a single antibiotic can apply selective pressure across many bacterial species, whether it's E. coli, Staphylococcus aureus and others, leading to widespread resistance to the one type of drug."
EspC is also a SPATE (serine protease autotransporters of Enterobacteriaceae), a group of toxins made by bacterial pathogens. There are two classes of SPATEs: one damages intestinal cells while the other promotes the growth of bacteria in the gut by manipulating immunity and breaking down protective mucins in the gut.
Sources: La Trobe University, Gut Microbes
