Escherichia coli O104:H4 is an enteroaggregative Escherichia coli strain of the bacterium Escherichia coli, and the cause of the 2011 Escherichia coli O104:H4 outbreak.^[1] The "O" in the serological classification identifies the cell wall lipopolysaccharide antigen, and the "H" identifies the flagella antigen.

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Escherichia coli O104:H4
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Gammaproteobacteria
Order:	Enterobacterales
Family:	Enterobacteriaceae
Genus:	Escherichia
Species:	E. coli
Strain:	E. c.  O104:H4
Trionomial name
Escherichia coli O104:H4

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Analysis of genomic sequences obtained by BGI Shenzhen shows that the O104:H4 outbreak strain is an enteroaggregative E. coli (EAEC or EAggEC) type that has acquired Shiga toxin genes, presumably by horizontal gene transfer.^[2][3][4]

Genome assembly and copy-number analysis both confirmed that two copies of the Shiga toxin stx2 prophage gene cluster are a distinctive characteristic of the genome of the O104:H4 outbreak strain.^[5][6] The O104:H4 strain is characterized by these genetic markers:^[6][7]

• Shiga toxin stx2 positive
• tellurite resistance gene cluster positive
• intimin adherence gene negative
• β-lactamases ampC, ampD, ampE, ampG, ampH are present.

The European Commission (EC) integrated approach to food safety^[8] defines a case of Shiga-like toxin-producing E. coli (STEC) diarrhea caused by O104:H4 by an acute onset of diarrhea or bloody diarrhea together with the detection of the Shiga toxin 2 (Stx2) or the Shiga gene stx2.^[9]

Prior to the 2011 outbreak, only one case identified as O104:H4 had been observed, in a woman in South Korea in 2005.^[10]

E. coli O104 is a Shiga toxin–producing E. coli (STEC). The toxins cause illness and the associated symptoms by sticking to the intestinal cells and aggravating the cells along the intestinal wall.^[11][12] This, in turn, can cause bloody stools to occur. Another effect from this bacterial infection is hemolytic uremic syndrome (HUS), which is a condition characterized by destruction of red blood cells, that over a long period of time can cause kidney failure.^[13] Some common symptoms of HUS are vomiting, bloody diarrhea, and blood in the urine.^[12]

A common mode of E. coli O104:H4 infection involves ingestion of fecally contaminated food; the disease can thus be considered a foodborne illness. Most recently in 2011, an outbreak of the O104:H4 strain in Germany caused the deaths of several people, and hundreds were hospitalised.^[14][15][12] German authorities traced the infection back to fenugreek sprouts grown from contaminated seeds imported from Egypt, but these results are debated.^{[citation needed]}

To diagnose infection with STEC, a patient's stool (feces) can be tested in a laboratory for the presence of Shiga toxin. Testing methods used include direct detection of the toxin by immunoassay, or detection of the stx2 gene or other virulence-factor genes by PCR. If infection with STEC is confirmed, the E. coli strain may be serotyped to determine whether O104:H4 is present.^[11]

E. coli O104:H4 is difficult to treat as it is resistant to many antibiotics, although it is susceptible to carbapenems.^[14]

Spread of E. coli is prevented simply by thorough hand-washing with soap, washing and hygienically preparing food, and properly heating/cooking food, so the bacteria are destroyed.^[16]