MICROBIOLOGY


systems improve, the burden of pathogenic E. coli infections can be significantly reduced, ensuring better public health outcomes.


Epidemiology and transmission E. coli is found in the gut of humans and animals and is ubiquitous, and as described is mainly an opportunistic pathogen; however, the infections it can cause are numerous. The overall disease incidence and epidemiology for E. coli related infections is unclear due to under-diagnosing, under- reporting, under-estimation, and unreliable data collection, particularly in resource-poor countries. However, they are considered the most common bacterial cause of infection globally in humans and are responsible for significant morbidity and mortality. Worldwide it is estimated that


virulence factors. Moreover, sub- species level identification aid in the epidemiology and disease incidence and can identify outbreaks caused by specific single strains. Serological latex agglutination analysis direct from bacterial culture can provide quick and reliable sub-species identification. The Prolex E. coli STEC O157 and Non-O157 STEC assays shown in Figure 3 are examples.17


These latex Fig 2. BBC News, reported 14 June 2024.16


there are about 404 million UTI cases each year with between 260 to 300 million of these cases being caused by E. coli. The prevalence of E. coli UTI is depicted in Figure 1 showing the organism is responsible for 75% and 65% of cases in uncomplicated and complicated UTIs, respectively.13 Outside of UTIs pathogenic E. coli


strains are commonly associated with numerous infections, and in particular with gastrointestinal, respiratory and bloodstream infections. Examples where epidemiological data are available include: n Over 220 million diarrhoea cases annually are attributed to ETEC infection with 75 million episodes attributed to children under five years of age, resulting in up to an estimated 42,000 deaths, with a substantial burden on children in low-income countries.14


n In developed nations, STEC is a leading cause of water and foodborne outbreaks, often linked to poor hygiene, contaminated produce, person-to-person contact, and contact with animal reservoirs such as cattle.15 Between May and June 2024 there were 275 cases of STEC caused by E. coli O145 which were geographically dispersed to all regions of England, Scotland, Wales, and Northern Ireland. This outbreak resulted in 81% reporting bloody diarrhoea, 122 hospitalised patients, seven confirmed cases of HUS and two reported deaths.15


Epidemiological analysis


indicated a potential for contaminated lettuce used in a nationally distributed sandwich manufacture to be the


probable cause (Fig 2). This resulted in significant precautionary recalls from sandwiches containing lettuce leaves from numerous supermarkets across the UK. The costs associated to this have not been published but are thought to be significant with resultant product recalls, medical costs, and public health investigations.


n Within the UK fiscal year 2023 to 2024, there were 42,224 reported cases of E. coli bloodstream infections. Resultant mortality rate was approximately 27%, leading to approximately 11,500 E. coli bacteraemia deaths.17


Diagnostics E. coli is one of the most commonly identified bacteria within the microbiology laboratory. Traditional methods for microbial culture, microscopy, and biochemical assays function as the mainstay for diagnosis to species level. In most infections, including UTIs and with the majority of bacteraemia cases, species-level identification supplemented with antimicrobial resistance biograms are sufficient to enable effective treatment. However, in severe E. coli infections and those with gastrointestinal infections indicating a potential outbreak, sub-species level diagnostics are usually required. On these instances the traditional culture- based methods, are supplemented by serological and molecular techniques, which provide sub-species level identification. This enables targeted response to the individual organism with gains detailed insights into the associated


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agglutination assays provide results within two minutes and have been developed by Pro-Lab Diagnostics to remove common cross reactions with similar ‘O’ and ‘H’ antigens found in E. hartmanii to sub-speciate all the common causes of STEC infections currently seen globally. Molecular assays have evolved to enable examination directly from faecal samples, either within a monoplex or multiplex format. An example is the Viasure E. coli RT PCR typing assay, which identifies individual EHEC, STEC, EPEC, ETEC, and EIEC strains directly from clinical samples to a molecular level.18 Currently, local identification past the genus level is difficult and individual serotype strain identification assays are usually undertaken within the reference laboratory. However, the increasing incidence trend is overwhelming reference laboratories and is considered unsustainable. There is a requirement for local laboratories to routinely provide diagnostic services to the sub-species level for E. coli. To help promote this, in November 2024 UK NEQAS sent out a non-scoring external quality assessment for four Non-O157 STEC samples for identification to 100 UK microbiology laboratories.19


We currently await the


findings of this important diagnostic exercise. Furthermore, studies are underway to evaluate suitable differential culture media and diagnostic assays to aid diagnosis to effectively enable local laboratory diagnosis. These findings will form the basis for a future article within Pathology in Practice in due course.


Vaccine development Efforts to develop vaccines against pathogenic E. coli strains have made considerable progress, including: n Development of ETEC vaccines targeting recombinant toxins and colonisation factors have shown partial efficacy in clinical trials.20


n UPEC vaccines designed to prevent recurrent UTIs have been highlighted by the WHO, which considers them to be one of the most important pathogens for vaccine research


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