A new analysis of deadly E. coli bacteria offers some ominous news about the bacteria. As this ScienCentral video explains, researchers have found there are different sub-types of the deadly E. coli bacteria and that the most dangerous type is becoming much more common in food borne outbreaks.
As investigators in 2006 worked to contain an outbreak of E. coli in spinach, food toxicology expert, Dr. Thomas Whittam at Michigan State University's National Food Safety and Toxicology Center, was among those that saw the outbreak continued an unsettling trend of doing more harm to its victims than previous outbreaks. He says, "The disease has gotten much worse than it was with a much greater fraction of people having to go to hospital and a much greater fraction of people that are seriously infected with the toxin."
Whittam, who has worked in this field for about 20 years, went to work genetically analyzing more than 500 E. coli 0157:H7 samples taken during outbreaks. E. coli is usually a harmless bacterium and is present in human digestive systems. But, E. coli 0157:H7 is a strain your body has trouble stopping. Its genome was first sequenced in 2001 but subsequent methods are much faster allowing for more analysis and comparisons among samples.
After analyzing E. coli 0157:H7 Whittam says, "We've been able to identify eight different groups and this group eight seems to be the most serious." Whittam and his team of researchers published their findings in the Proceedings of the National Academy of Sciences online early edition for the week of March 10, 2008.
Whittam's analysis is also showing a shift in how often each sub group is showing up. He says the group eight has, "increased in frequency in North America over 50 percent over the last two years. The most common group, which scientists call clades, number two is decreasing in how often it shows up on illness outbreaks.
In the paper, Whittam wrote, "These 2006 outbreaks caused reportable illnesses in more than 275 patients and resulted in remarkably high rates of hospitalization (average 63%) and HUS (average 13%), a rate that is 3 times greater than the average HUS rate for 350 outbreaks." HUS, or hemolytic uremic syndrome, can occur after food poisoning from E. coli and can lead to kidney shutdown and death. One person died from the 2006 spinach outbreak.
Despite the detailed genetic analysis, Whittam says clade 8 remains a mystery, explaining, "We really don't know that much detail on its ecology." E. coli 0157:H7 outbreaks were mostly commonly associated with beef, but recent outbreaks have included spinach and lettuce. Whittam says the E. coli responsible for those outbreaks were from clade 8. Whittam says of clade 8 E. coli, "It seems to be specialized in some ways in its ecology, but we're not sure exactly what that advantage is. The other thing is it does have a different production of the shiga toxins, and that seems to give it some enhanced seriousness in the infection."
The method Whittam used to run genetic tests on more than 500 samples of E. coli is much faster than previous methods. Through the use of a novel procedure he and his team were able to run tests in a few days that previously took months. He says they're looking to speed the process further, adding, "The main advantage will be to allow us to rapidly identify the source, [of] outbreaks." He says outbreaks in vegetables are particularly time challenging adding, "We'd like to be able to do that very very quickly and that's what this new method …will allow those identifications and sources to take place."
This research was published in the Proceedings of the National Academy of Sciences online early edition for the week of March 10, 2008 and was funded by the National Institutes of Health.