PRO/AH/EDR> E. coli EHEC - UK (03): O183, RICHIESTA DI INFORMAZIONI

E. COLI EHEC - UK (03): O183, REQUEST FOR INFORMATION
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Date: Wed 2 Aug 2023
Source: Food Safety News [edited]
https://www.foodsafetynews.com/2023/08/rare-e-coli-type-behind-deadly-uk-outbreak-2-dozen-sick/

Rare _E. coli_ type behind deadly UK outbreak; 2 dozen sick
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A person has died in an _E. coli_ outbreak being investigated by health authorities in the UK. The Food Standards Agency (FSA) and UK Health Security Agency (UKHSA) are trying to find the source of the ongoing Shiga toxin-producing _E. coli_ (STEC) [also known as enterohemorrhagic _E. coli_, EHEC] O183 outbreak with the help of other public health agencies. There are 24 cases in the UK, with 19 in England, 2 each in Northern Ireland and Scotland, and 1 in Wales since May 2023. For patients with available information, onset dates range from 23 May 2023 to 2 Jul 2023.

Patients have reported severe symptoms such as bloody diarrhea. Eight sick people visited hospitals for their symptoms, and 6 were hospitalized. Of the patients, 12 are male, and 12 are female. Ages range from under 1 to 74; the most affected age group is children 9 years old and younger. Epidemiological investigations are ongoing, but based on initial work, no standout food vehicle of infection exists. From patient interviews, sick people reported consuming hard cheese in a grated format. Strawberries, cucumbers, peppers, and watermelon have also been mentioned.

Amy Douglas, UKHSA incident director, said: "The UKHSA has identified an outbreak of a rare form of EHEC, with most cases seen in children. The outbreak's source has not yet been identified, but we are working with partners, including the Food Standards Agency, to investigate. Washing hands thoroughly with soap and water and ensuring to help young children with handwashing is the best way to stop the bug spreading. Children under 5 should not attend school/nursery/group childcare until they have been free of sickness or diarrhea for 2 days. Visits to hospitals or care home settings should be avoided if you are feeling unwell."

One person developed Hemolytic Uremic Syndrome (HUS), and one death is linked to the outbreak, although it is unclear if the person died because of or with EHEC. HUS is a severe complication usually associated with EHEC infections that causes kidney failure.

_E. coli_ O183 is an extremely rare serotype, with only 15 cases in the UK since 2016. Transmission can occur through direct or indirect contact with animals or their environments, contaminated food or water consumption, and person-to-person spread.

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Communicated by:
ProMED

[The O183 serotype is quite unusual. That the cases were fairly wide-spread suggests a foodborne source. ProMED awaits more confirmation regarding the organism (which has been sometimes misidentified), the scope of the outbreak and the vehicle of transmission.

The following discussion on O, the somatic antigen, was extracted from https://metacyc.org/META/NEW-IMAGE?type=PATHWAY&object=PWY-8234 (references can be found at the original URL - Mod.LL):

'The lipopolysaccharide (LPS) is one of the major structural and immunodominant molecules of the outer membrane in Gram-negative bacteria. It consists of 3 moieties: lipid A, which anchors LPS into the membrane; the core oligosaccharide, which contributes to membrane stability; and the O antigen, which is a polysaccharide that extends away from the cell surface. The structure of the O antigen consists of a polymer of oligosaccharide repeating units normally containing 2 to 8 sugar residues.

The presence of an O antigen is essential for survival of bacteria in their natural environment and plays a role in bacterial virulence. There is direct evidence that the loss of O antigen makes many pathogens, such as _Escherichia coli_, _Shigella flexneri_, _Francisella tularensis_, and _Yersinia enterocolitica_, serum sensitive or otherwise seriously impaired in virulence [Pluschke83, Bengoechea04, West05, Plainvert07, Raynaud07].

The synthesis and translocation of the O antigen can occur through 3 distinct pathways: the flippase/polymerase (Wzx/Wzy)-dependent pathway, the ABC transporter-dependent pathway, and the synthase-dependent pathway [Heinrichs98, Raetz02]. Among them, the Wzx/Wzy-dependent pathway accounts for the synthesis of most heteropolysaccharides [Guo08].

The genes specific for _Escherichia coli_ and _Salmonella_ O antigen synthesis are generally present as a gene cluster in the chromosome, called the O antigen gene cluster, which maps between the galF and gnd genes.

_Shigella_ is a well-known human pathogen that causes diseases such as diarrhea and bacilliary dysentery (shigellosis). It is closely related to _Escherichia coli_, and while was given its own genus in the 40s, sequence-based phylogeny suggests that the genus may have to be re-incorporated into _Escherichia coli_.

The _Shigella_ serotypes were named B/D/F/S for variations found in the 4 species _Shigella boydii_, _Shigella dysenteriae_, _Shigella flexneri_, and _Shigella sonnei_, respectively [Liu08].

The repeat unit is very similar to that produced by _Shigella boydii_ O6 but contains an additional ribofuranose residue [Senchenkova05]. Inactivation of the extra glycosyltransferase gene ( wbaM) found in the cluster of _Shigella boydii_ O10 resulted in production of the _Shigella boydii_ O6 O antigen repeat unit by the mutant, indicating that the gene encodes the enzyme responsible for the transfer of the ribosyl residue. While D-ribofuranose (D-Ribf) is present in the O antigens of several bacterial strains (such as the _Escherichia coli_ serogroups O5, O20, O54, O105, O114, O153, O178, O183 and O185), ribofuranose transfer reactions are not well characterized, and even though the donor in these reactions is assumed to be a nucleotide diphosphate form, as is standard in this type of reactions, this has not been verified. As of 2020 WbaM is the only enzyme catalyzing a ribosyltransfere reaction that has experimental evidence.

In 2008 a Shiga toxin 1 (Stx1)-producing _E. coli_ strain that didn't cross react with any known _E. coli_ antisera was isolated from a patient with hemorrhagic colitis in Japan. Sequencing of its O antigen gene cluster has revealed that it is identical to that of _Shigella boydii_ O10 [Iguchi11]. The new _E. coli_ serogroup was originally named OSB10, but later renamed O:183 [Iguchi15]. As could be expected, the structure of the O antigen repeat unit was also shown to be identical between the 2 strains [Knirel16]." - Mod.LL