Sunday, January 22, 2012

Would you like some E. coli with that?

An epidemic of bloody stools and failing kidneys, some with hemolytic uremic syndrome (HUS) appeared in Germany in May 2011 and subsequently 15 other countries. By late July when the epidemic had subsided, a total of 3,816 cases - including 54 deaths - were reported in Germany, 845 of which included HUS. Rasko and colleagues cultured E. coli bacteria isolated from a 64 year old woman from Hamburg, Germany, who did not develop HUS. They characterized this bacterium, designated C227-11, as enteroaggregative, which means a gut pathogen that aggregates and forms “biofilms” that are resistant to treatment.

They sequenced the bacterium’s genome and found it was a unique strain of the O104:H4 serotype of E. coli bacteria, distinguished by possession of a prophage ( ) producing the Shiga toxin. Shiga toxin binds to cells, inhibits protein synthesis, and kills by inducing apoptosis [review]. The O104 serotype is rare; the most frequent cause of HUS worldwide is the shiga-toxin–producing E. coli O157 (Tarr 2005).
Although they isolate only one strain themselves, they analyzed also 3 additional sequences from the current outbreak that had been made public (that’s data mine-ing!) together with 7 other O104:H4 serotype isolates, all from Africa, and 4 other reference strains. The authors conclude that the outbreak was caused by a difficult (enteroaggregative) strain made more virulent by its acquisition of the Shiga toxin gene in addition to antibiotic-resistance and “additional virulence and antibiotic-resistance factors”. Rohde and colleagues reached the same conclusion using "rapid, bench-top DNA sequencing technology, open-source data release, and prompt crowd-sourced analyses".

Where did the E. coli O104:H4 come from? A subsequent publication reported the results of trace-back and –forward investigations by Buchholz and colleagues who analyzed 26 HUS patients and 81 healthy controls. They concluded that despite only about a quarter of the patients recalling in exploratory interviews having eaten bean sprouts during the 14 days before the onset of illness, 100% of these illnesses were attributable to the consumption of sprouts – and not other raw foods such as tomatoes or cucumbers or lettuce – at a particular restaurant, and for other patients, sprouts obtained from a single, common supplier (figure).

N Engl J Med. 2011 Aug 25;365(8):709-17. Origins of the E. coli strain causing an outbreak of hemolytic-uremic syndrome in Germany. Rasko DA, Webster DR, Sahl JW, Bashir A, Boisen N, Scheutz F, Paxinos EE, Sebra R, Chin CS, Iliopoulos D, Klammer A, Peluso P, Lee L, Kislyuk AO, Bullard J, Kasarskis A, Wang S, Eid J, Rank D, Redman JC, Steyert SR, Frimodt-Møller J, Struve C, Petersen AM, Krogfelt KA, Nataro JP, Schadt EE, Waldor MK.