RESEARCH DETAILS

Enteropathogenic E. coli (EPEC)

Diarrhoeal disease

Up to 2 billion people each year have diarrhea. Tragically, it has severe consequences for infants, particularly those under 2 years old. In fact, the second leading cause of infant death  across the world is diarrhoea -  responsible for over 1.5 million deaths annually. Death caused by diarrhea, which is most common in developing countries, are almost always preventable, often due to dehydration due to fluid loss. Infectious diarrhoeal disease is caused by viruses, bacteria and parasites and scientists study these pathogens to try and understand the diseases that they cause and how best to combat them. Common pathogens that cause diarrhea include enteropathogenic E. coli, - the nasty bug that we work on:

What is EPEC

Enteropathogenic E. coli (EPEC) is a virulent strain of E. coli that causes disease in humans. It was the first strain of E. coli to be associated with diarrhea, isolated from an outbreak in a pediatric nursery in London (UK) by John Bray and colleagues in 1945. The term ‘enteropathogenic E. coli’ was coined in a publication by  Neter et al in 1955 to indicate E. coli linked to childhood diarrhoea.  EPEC targets our small intestine following ingestion of contaminated food or drink and causes severe watery diarrhea, particularly among infants in developing nations. EPEC is one of the most prevalent causes of diarrhoea in infants, particularly those under 6 months old, and is responsible for up to 30% of  cases in developing countries. Although EPEC is not so prevalent in developed countries, it does occasionally cause sporadic outbreaks, particularly in child-care centres

EPEC is a member of a closely-related family of bacterial pathogens that  induce an  ‘Attaching and Effacing’ (A/E) lesion on the surface of intestinal epithelial cells. This  histopathological change is the defining feature of all A/E pathogens and is believed to be the main  cause of diarrhoeal symptoms. Other A/E pathogenic bacteria  include EHEC 0157:H7 (enterohemorrhagic E. coli), which causes disease in humans and cattle and is a particular problem in developed nations including the UK. Another A/E pathogen, Citrobacter rodentium causes disease in mice and are often used in animal model studies to study A/E pathogen disease in vivo (as unfortunately there is no animal model system for EPEC - and human volunteers can be expensive!). Below you will see the type of lesions that EPEC causes on the surface of our intestinal cells:

Normal microvilli Uninfected Intestinal Cell Surface Loss of microvilli EPEC infected intestinal cell surface

How does EPEC cause disease?

When ingested, EPEC attaches to the surface of small intestinal cells by using a number of well characterised adhesins. Most typical EPEC carry genes that encode the bundle forming pilus (BFP), a very important virulence factor that aids in the first steps of host cell attachment. The BFP also enable the bacteria to form dense ‘microcolonies’ -  three dimensional clusters of bacteria that are often used as a diagnostic feature to identify typical EPEC stains. The reason for microcolony formation is not entirely clear. The Donnenberg Lab has extensively studied the BFP and revealed it to be a highly dynamic multi-protein structure. It has one of the most powerful molecular motors known in the living world!.

Following initial attachment, EPEC uses a sophisticated molecular machine called a type three secretion system (T3SS) to physically inject effector proteins directly into the cells of its host. EPEC injects over 20 known effector proteins into its host cells (see effector section). Unlike invasive pathogens such as Salmonella and Shigella, EPEC does not enter host cells but usually remains extracellular and therefore relies on its effector proteins to do most of the work during infection. The collective activities of the effector proteins lead to diarrhoea, which  in the case of EPEC  is probably a combination of destruction of intestinal microvilli,  intestinal tight junctions and an inhibition of water reabsorption. Our lab has shown that all three diarrhoeal processes are controlled by the concerted efforts of EPEC’s effectors (see below).

EPEC’s effector proteins........

Effector proteins often have subtle biochemical functions within the host cell that often cause dramatic  morphological events. Indeed, these phenotypes are the hallmarks of EPEC disease and include the loss (effacement) of  intestinal microvilli and  the formation  of an actin-rich pedestal underneath adherent bacteria (see images). Other effects of EPEC’s injected proteins include inhibition of nutrient/water transporter function, mitochondrial dysfunction, inhibition of inflammation and disruption of epithelial tight junction. The actin-rich pedestal is induced by the injected effector Tir and enables the bacterium to attach very strongly to the host cell surface. Other effector functions are given in the effector section. The functions of EPEC effectors is a fast moving topic and provides important clues about how bacteria can  manipulate the host cell often by mimicking host proteins. In addition, bacterial effectors are even providing clues about unknown eukaryotic biochemical pathways or new functions of eukaryotic proteins, of which there are now many examples. Several other excellent labs work on EPEC and A/E pathogen effectors including the Labs of Akio Abe, Michael Donnenberg, Gail Hecht, Brett Finlay, Chihiro Sasakawa, Neal Alto, Jack Dixon, John Leong, Gadi Frankel, James Kaper, Elizabeth Hartland, Roy Robins-Browne and Eric Oswald.   

The diverse and overlapping functions of EPEC effector proteins within the host cell

Taken from Dean and Kenny (2009)

Specific Research Projects in the lab

The EspF effector and the host nucleolus

The nucleolus is a eukaryotic structure with the cell nucleus that is primarily responsible for ribosome biogenesis. A feature common to almost all viruses is that they target their viral proteins to the nucleolus, although it is not clear why they do this. Our lab has recently shown that the EPEC effector EspF targets the nucleolus (PLOS Pathogens publication) and this leads to nucleolar alterations. EspF is the first bacterial protein known to target the nucleolus during bacterial infection. In the same study, we also show that the host’s mitochondria kinetically regulate when EspF is able to target the nucleolus. This is a neat mechanism as the bacterial pathogen exploits a host organelle to control the functions of its effector proteins. Whether viruses utilize this mechanism remains to be seen but a number of viral proteins are known to target both the mitochondria and nucleolus, like EspF.  Click here to view more info, the images and videos relating to this project.

If you would like to see more videos and images click here to go to the nucleolar page

The nucleolar work was presented at the Sub Nuclear Structures and Disease Conference at the Wellcome Trust Conference Centre, Hinxton - 27th-30th July 2010

From our PLOS Pathogens paper..........

Exploitation of host mitochondria to kinetically regulate the cellular locations and functions of a bacterial effector

Model:

EspF performs its numerous transient functions in the cytoplasm and is then rapidly sequestered into mitochondria, ensuring its functions are not overtly deleterious to the host cell. Much smaller amounts of EspF are subsequently delivered into the nucleolus later in infection.