General News: German E Coli Outbreak

Recent news about the German E coli O104:H4 outbreak has come back into the news, with reports of it in France and other European nations. It began when people in Germany were admitted to hospitals with bloody diarrhea in May 2011, and within a month, over 3700 cases have been reported with 42 deaths. The source of the E coli is likely to be bean sprouts according to the WHO.

E coli is a natural organism of human beings, normally residing in our gut. In fact, a very large portion of human feces is made up of E coli. They are believed to provide some health benefit to humans, perhaps by pre-binding to our intestines they prevent other bacteria from attaching to our intestinal cells. Normally E coli is harmless but sometimes, they can become pathogenic by getting infected with a virus known as a bacteriophage. This specific phage produces Shiga toxin, which is responsible for the severe diarrhea and kidney damage observed in infected patients who develop hemolytic uremic syndrome (HUS). Interestingly, this phage accidentally picked up the Shiga-toxin gene from Shigella, another pathogenic bacteria, while infecting it many years ago.

It is believed that antibiotics may be contributing to the spread of this phage, making it extremely difficult to treat patients who have this disease. Normally under non-stressed conditions, some phages lie lurking in the genome. But when bacteria are stressed by mutagens or even antibiotics, they undergo something known as the SOS response, which is essential a Hail-Mary attempt to survive. Unfortunately, this SOS response also activates the lurking phage, allowing it to exponentially divide and eventually causing the cell to burst, leaking hundreds of phage as well as Shiga toxin into the bloodstream. This is one reason why E coli infections are not usually treated with antibiotics. The other reason is antibiotics also target normal E coli in the gut, removing them and providing other bacteria the opportunity to bind and wreck havoc to the gut.

E coli also finds a home in many of the farm animals we raise, in particular cattle. It is believed that the constant application of antibiotics to cattle is contributing to pathogenic E coli. Firstly, it promotes the acquisition of multiple antibiotic resistant genes. Secondly, it promotes an explosion of phage throughout the cow gut, allowing it to infect many other E coli cells. Since cows don’t get sick from Shiga-toxin producing E coli, it is difficult to tell which cows are affected other than be testing their feces. Indeed, it has been found that over a half of cows in North America possess virulent strains of E coli.

The one thing that has people worried is that the German strain of E coli is new. While it produces Shiga-toxin, it also has multiple antibiotic resistant genes so even if we wanted to try to kill them using antibiotics, we would have a hard time doing is. In addition, bacterial species are very good at picking up genes from other bacteria, so one worry is that these antibiotic genes could transfer to a different bacteria. The other worry is that this bacteria also has some enteroaggregative E coli properties (probably from that gene swapping ability I mentioned earlier), which means it can aggregate cells on a dish. This combination of both Shiga-toxin and enteroaggregative properties has not been observed before, and so has scientists worried.