A molecule called N-glycolylneuraminic acid (Neu5Gc), a type of glycan, helps a toxin from certain types of E. coli to target human cells, according to a team of international researchers.
"Ironically, humans may set themselves up for an increased risk of illness from this kind of E. coli bacteria present in contaminated red meat or dairy, because these very same products have high-levels of Neu5Gc," said researcher Ajit Varki from the University of California, San Diego. "The Neu5Gc molecule is absorbed into the body, making it a target for the toxin produced by E. coli."
The researchers report that sites where Neu5Gc has been incorporated into the human body are related to binding of a bacterial toxin called subtilase cytotoxin. "When the toxin binds to the non-human Neu5Gc receptors, it can result in serious food-poisoning and other symptoms in humans," said Varki.
The research also highlights the processing of dairy and meat should destroy the bacteria. Humans do not naturally produce Neu5Gc.
Building the science
Varki and his colleagues at the UC San Diego reported five years ago how Neu5Gc is absorbed into human tissues as a result of eating red meat and milk products.
The study was reportedly the first to investigate human dietary absorption of the Neu5Gc glycans found naturally in red meats.
“Ironically, foods rich in Neu5Gc are the most common source of Shiga toxigenic Escherichia coli contamination,” wrote the researchers. “Thus a bacterial toxin's receptor is generated by metabolic incorporation of an exogenous factor derived from food.”
The research was funded by the National Institutes of Health, and by Australia's National Health and Medical Research Council.
Red meat concerns
Red meat has been the subject of unfavourable reports concerning a potential link to increased risks of certain cancers.
According to results from the National Institutes of Health (NIH)-AARP (formerly the American Association for Retired Persons) Diet and Health Study, a high intake of red and processed meats was associated with a 20 per cent increase in the risk of lung and colorectal cancer.
Moreover, a study from the World Cancer Research Fund's (WCRF) concluded that high consumption of red and processed meat was associated with a 30 per cent increase in the risk of colorectal cancer.
Published online ahead of print, 29 October 2008, doi: 10.1038/nature07428
“Incorporation of a non-human glycan mediates human susceptibility to a bacterial toxin”
Authors: E. Byres, A.W. Paton, J.C. Paton, J.C. Lofling, D.F. Smith, M.C.J. Wilce, U.M. Talbot, D.C. Chong, H. Yu, S. Huang, X. Chen, N.M. Varki, A. Varki, J. Rossjohn, T. Beddoe