Deep throat reveals secrets about bacteria

Bacteria living in the esophagus may be the
cause of certain diseases

By Owen Dyer

Every doctor knows that bacteria don't infect the esophagus. Except, apparently, they do. And that can have major implications for our understanding of gastroesophageal reflux disease (GERD) and its potentially lethal complications, according to a study published in the March 23 issue of the Proceedings of the National Academy of Sciences.

The traditional petri dish approach of finding bacteria has rarely produced anything from the esophagus that could be cultured. Textbooks have never described microbes in the esophagus. But New York University School of Medicine scientists used the more modern polymerase chain reaction (PCR) technique to greatly amplify snippets of DNA extracted from biopsies of tissue. The biopsies were taken from the distal esophagus in four healthy patients. They found 95 species of bacteria.

With hindsight, the finding isn't that surprising. It's well known that fungal infections such as candidiasis can occur in the esophagus, as can herpes simplex virus. Use of broad-spectrum antibiotics, notably tetracycline, is known to favour the growth of Candida albicans in the esophagus.

"People thought that the esophagus wasn't hospitable to bacteria," says study author Dr Martin Blaser, Professor of Microbiology at New York University. But bacteria have now been found in deep-sea vents, hot springs, volcanoes and other extremely harsh environments. "By comparison, the esophagus seemed much more hospitable," adds Dr Blaser.

It's only 20 years since the medical community was surprised to learn that the bacterium H pylori can survive in the stomach, and actually plays a major role in ulceration. Later, Dr Blaser was one of the scientists who established an association between H pylori and some stomach cancers. The potential implications of these new findings regarding Barret's esophagus and esophageal cancer are obvious.

Lead author Dr Zhiheng Pei also draws a parallel with colon cancer: "Animal studies suggest that inflammation and normal bacteria work in concert to cause colon cancer. Esophageal cancer arises in an area of the esophagus where chronic inflammation is occurring."

Dr Pei says he saw bacteria colonizing the surface of the esophagus, proving that the micro-organisms were not simply passing through on their way to another destination. Sixty percent of the 95 bacterial species identified were present in all four of the patients, suggesting that these species are common in all people. Most of the species were closely related to bacteria known to inhabit the mouth, but some were not. Indeed, "some esophageal bacteria may be unique," notes Dr Pei.

The researchers plan to replicate their study using samples taken from GERD patients. They expect to find even more bacteria in unhealthy esophageal tissue.

"We are operating in the framework of the 'microbiome' ? a term coined by Nobel Laureate Joshua Lederberg," says Dr Blaser. "It means that microbes are part of us, part of our identity. They aren't just passengers," he explains, "but are, in essence, metabolic and physiologic compartments of the human body."