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E. coli
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- 1Define the taxonomy of e. coliGram negative bacillus belonging to the family Enterobacteriacae
There are 7 species in the genus
Escherichia
E. coli/Shigella is the species usually isolated from human clinical samples
Facultative anaerobe
Usually motile (note EIEC/Shigella variants) - 2How is e. coli typed?Serotyping:
Somatic (O) antigens: polysaccharides of LPS
Flagella (H) antigens
Genotyping:
Phylogenetic grouping: combination of MLEE/MLST/ribotyping/whole genome data, or by rapid multiplex PCR.
Up to 6 phylogenetic groups: A, B1, B2, C, D, E - 3Name the e. coli pathotypesEnterotoxigenic (ETEC)
Enteropathogenic (EPEC)
Enteroaggregative (EAEC)
Enteroinvasive (EIEC/Shigella)
Shigatoxic (STEC)/Enterohaemorrhagic (EHEC)
Diffusely aggregative (DAEC) - 4Describe ETECETEC is an important cause of childhood diarrhoea in developing countries, and also travellers’ diarrhoea
It is a food/water borne infection
Incubation period varies from hours to 2 days - 5Symptoms of ETEC?nausea, vomiting, abdominal cramps, and non-bloody watery diarrhoea resembling cholera, lasting up to 5 days
- 6Pathogenesis of ETEC?Colonisation by a diverse (20+) collection of plasmid or chromosomal encoded pili/fimbrae adhesins (which are immunogenic), secreted exoproteins (e.g. EtpA), outer membrane proteins, and regulator proteins (toxin secretion).
Diarrhoea is caused by either one or both plasmid encoded enterotoxins:
Heat labile toxin (LT)
Heat stable toxin (ST) - 7Describe the heat labile toxin (LT)LT is is very similar to cholera toxin.
Classic A/B subunit enterotoxin secreted by T2SS.
B subunit binds to GM1 and is transported to the golgi apparatus.
A subunit activates G protein which activates adenylcyclase and cAMP accumulation.
Diarrhoea results from passive Na+ and water loss - 8Describe heat stable toxin (ST)ST is a small heat stable peptide toxin that resembles the mammalian peptide hormone guanylin.
ST bind to, and activates the guanylin receptor.
This causes accumulation of cGMP also leads to phosphorylation activation of CFTR and associated diarrhoea. - 9What does EPEC cause? And atypical EPEC?Major cause of infantile diarrhoea in developing countries.
Atypical EPEC lacks bundle forming pili (BFP), but is found to be an important cause of infantile diarrhoea in developed countries. - 10EPEC is defined by what? Typical strains carry what?The ability to cause the attaching and effacing effect on enterocytes.
The plasmid (EAF) encoded EPEC adherence factor plasmid that encodes the bundle forming pili (BFP). - 11Molecular pathogenesis of EPEC?Carries an adhesin, its own receptor and the means to inject the latter into host cells. Attaches to the infected enterocytes, effacement of microvilli, and forms a “pedestal” like cellular structure by the host cell.
- 12What is the pathogenicity coded on?A 41-gene pathogenicity associated island (PAI) known as the Locus of Enterocyte Effacement (LEE).
- 13What does LEE encode?T3SS, major effectors: the outer membrane bound effector intimi and translocated intimin receptor, regulators, and other translocated effectors.
- 14The EPEC T3SS is characterised by what?The long filamentous “needle” compose of EspA subunits.
The host cell pore forming complex formed by EspB and EspD, through which the EspA filament translocates effectors. - 15Cellular pathogenesis of EPEC?Exhibits biofilm and localised attachment, associated with the expression of BFP, which bundle to form rope like structures.
- 16What else is BFP important in? What may the D be caused by?BFP is also thought to be important in the initial contact between EPEC and enterocytes, and atypical EPEC lacking BFP are thought to be less pathogenic.
D may be caused by Loss of microvilli,
Loosening of tight junctions and/or
Fluid secretion. - 17Define EAEC including what its associated withRelatively recent (1987) addition.
An “emerging” pathogen that causes diarrhoea in children in both industrialised and developing countries, as well as travellers’ diarrhoea.
Symptoms include colic, bloody or mucous diarrhoea.
Chronic infection in children (asymptomatic or symptomatic) can result in growth retardation.
In immunosuppressed patients e.g. HIV, diarrhoea can persist (chronic).
EAEC infection is associated with raised intestinal IL-8 production. - 18EAEC infection is characterised by what?Aggregative adherence (2 dimensional clustering) to the intestinal mucosa (or cultured cells, glass slide, plastic) mediated by Aggregative Adherence Fimbrae (e.g. AAF/I, AAF/II), although some aggregative strains lack AAF.
- 19What is a defining characteristic of EAEC?Presence of AggR
- 20What enterotoxins does EAEC produce?EAST - similar to ETEC heat stable toxin
Pet - a cytoskeleton toxin
ShET (Shigella enterotoxin) - proinflammatory, inducing IL-8 production from epithelial cells.
Dispersin - disrupts the aggregation and facilitates horizontal spread of EAEC. - 21Pathogenesis of DAEC?They are characterised by the presence of the afa/dra/daa family of genes that encode very similar group of adhesins. The adhesions bind to DAF which activates intracellular signal transduction cascades with the following effects:
Microvilli elongation
Microvilli loss
IL-8 production and polymorph transepithelial migration
Internalisation of DEAC - 22Secreted autotransporter cytotoxin (Sat) production causes what?Programmed epithelial cell death - permeability and inflammation
Tight junction associated protein rearrangements - 23Define EIEC/shigella, including phenotypical characteristicsGenetically closely related and can share a number off distinctive phenotypical characteristics (loss of motility, negative lysine carboxylase, lactose non-fermentative) including pathogenesis that distinguish them from other E. coli, and also by IpaH gene PCR
- 24EIEC and shigella can be separated by which tests?Serotyping, non-gaseous glucose fermentation, salicin fermentation, aesculin hydrolysis
- 25Pathogenesis of shigella?Low infection dose (200-500 cfu), EIEC/Shigella invade the colo-rectal intestial mucosa, causing epithelial damage.
Shigellosis is an epithelial disease – systemic infection is exceptionally rare. - 26Pathotype is defined by?The presence of a large virulence plasmid (pINV), and the presence of IpaH genes both on their chromosomes and pINV
- 27pINV encodes what?a T3SS and its effectors (IpaA/B/C, IpgD), plus IcsA
- 28What does the IpaB protein cause?Triggers cytoskeleton rearrangements for cell entry
Pore formation with IpaC for escape into cytosol
Causes macrophage apoptosis (in the case of swallowed by the “wrong” cell) and release IL-1β and IL-18 - 29Define STEC/EHECProduce shiga toxin, STEC less severe than EHEC although associated with haemolytic uraemic syndrome HUS.
HUS carries a 12% risk of death or end-stage renal failure, and 25% of surviving patients will have long-term renal impairment. - 30Name the most common serotype of EHEC. Infective dose of STEC/EHEC? Found where?0157:H7
<100 cfu
Farms, various animals, meat, fruit - 31What shiga toxins does it produce?Stx1, Stx2, Stx2c
- 32State an ExPEC pathogenUropathogenic E. Coli (UPEC), UTIs, such as isolate st131
- 33UPECs possess PAIs that encode what? Toxins?pap, hly, cnf1.
E.coli alpha haemolysin, cytotoxic necrotising factor, Sat are found in different percentage of UPEC subgroups - 34UPEC pathogenicity?Type 1 fimbriae, toxins
- 35Another ExPEC strains?MNEC, most common cause of Gram negative neonatal meningitis, express S fimbriae and most also express P fimbriae.
Membrane adhesion molecules and toxins. - 36—
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- Human Pathogens Karteikarten am E. coli, erstellt von Zack Cooper am 27/12/2018.
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