L17: E Coli Flashcards
What is E Coli?
Escherichia Coli
Gram Negative Rods (red/pink) staining
Typically lactose fermenting
Facultatively anaerobic
Often Motile
Numerous serotypes–> Different antigens (O, K F, H)
Consitutuent part of large bowel, microbiota of many animals including human
What is meant by ‘one health’ ecology of E Coli?
E Coli spread between animals, humans and the environment –> interconnectedness
Includes pathogenic and resistant strains
Challenge of controlling spread–> antibacterial resistance
What is the structure of an E Coli under the microscope?
Rod shaped
Plasma membrane, cell wall, nucleoid, ribosome
How can E Coli be identifies in the laboratory?
E Coli uses sugar lactose as an energy source
Produces lactic acid as waste product
MacConkey agar contains lactose and a pH indicator
Goes red with lactic acid
Others such as Pseudomonas aeruginosa–> non lactose fermenting–> yellow colonies
How are the many different species of E Coli known about?
Different typing technologies discovered different species
1) Serology–> using antibodies to detect the different antigens- O, K, F and H
2) Metabolic profiling–> variation in biochemical pathwaus
3) Genomic diversity –>
- DNA hybridisation,
- multi-locus enzyme electrophoresis (MLEE),
- multi-locus sequence typing (MLST),
- whole genome sequencing
What is an added advantage of genome sequencing?
Determine strain
Also can determine who passed it on to who
What are the different antigens present on E Coli?
O–> lipopolysaccharide antigen
–> Body detect O antigen (PAMP) –> Inflammatory response
–> Different O antigens on different strains allows for invasion–> evades immune system
H–> antigen on flagellum
K–> Capsule antigens
F–> Fimbriae antigens
What did whole genome sequencing show?
1509 EColi cultures were sequences 70,000 different genes identified 885 genes present in all 1509 isolates --> 885 genes say it is E Coli --> Rest unknown function--> may make them pathogenic
What is meant by E Coli in health and disease?
EColi found in the large bowel–> normal part of gut flora
Possibly protects against invasion by pathogenic species such as Salmonella
Can also cause:
- Intestinal infections
- Toxin-mediated disease
- Extra-intestinal infections
What are some of the extra-intestinal infections?
Urinary tract Intra-abdominal Biliary tract Bloodstream infection Neonatal meningitis
What causes E Coli to causes disease?
Different strains have different virulent factors
What are the causes of diarrhoea linked to E Coli?
6 different pathotypes of diarrhoeagenic E Coli
- -> Enterotoxigenic E Coli (ETEC)
- -> Enteropathogenic E Coli (EPEC)
- -> Enteroaggregative E Coli (EAEC)
- -> Enteroinvasive E Coli (EIEC)
- -> Diffusely adherent E Coli (DAEC)
- -> Shiga toxin-producing E Coli (STEC) aka Verocytotoxin-producing E Coli (VTEC) or Enterohaemorrhagic E Coli (EHEC)
Which ones are the most common in children? Immunocompromised patients?
EPEC and EIEC–> common in children in developing country
EAEC most common in immunocompromised
What is Enterotoxigenic E Coli?
Diarrhoeal illness–> Travellers’ diarrhoea
Low income countries
Faeco-oral transmission
ETEC produces two toxins–> Heat stable toxin (ST) and Heat-labile toxin (LT)
How does enterotoxigenic E Coli cause diarrhoea? What other symptoms? For how long?
Produced two toxins–> heat-stable toxin (ST) and heat-liable toxin (LT)
Stimulates lining of intestines causing them to secrete excessive fluid–> profuse watery diarrhoea and abdominal cramping
Symptoms–> Nausea with/without vomiting, fever, chills, loss of appetite, headache, muscle aches and bloating
Last 3-4 days (onset 1-3 days after exposure)
How does enteropathogenic E Coli cause diarrhoea?
- Localised effacement of microvilli from enterocytes
- Attaches to host surface, forms channels via Type III mediated secretion machinery forming translocation tube
- Bacterial proteins sent into cell including Tir receptor (bacterial receptor)
- Tir receptor embeds into plasma membrane of infected cell
- Intimin secreted by bacteria EColi attached to pathogen derived protein–> Tir receptor
- EColi attached to membrane
- Signalling pathway –> reorganisation of host actin cytoskeleton–> formation of pedestal base
What does Shiga toxin-producing E Coli (STEC) cause?
Haemorrhagic colitis (bloody diarrhoea) and haemolytic uraemic syndrome (acute renal failue, haemolytic anaemia and thrombocytopenia)
How does the STEC work?
- 5 beta subunits associated with alpha subunit form toxin
- Bind to Globotriaosylceramide (Gb3) on host cell surface
- Toxin is endocytosed and transported to the golgi apparatus and ER
- Intracellular transport–> A chain cleaved into A1 (enzymatically active) and A2
- Kept together by a disuphide bond until they reach the ER
- A1 fragment is released and translocated to the cytosol
- A1 inactivates ribosomes–> inhibiting protein synthesis–> results in cell death
What are a few of the STEC outbreaks? Why?
Oregon and Michigan 1982–> meat from a fast food restaurant
Scotland 2016–> Dunsyre Blue Cheese–> Unpasteurised cows milk–> cows faeces in milk
Germany 2011–> Contaminated bean sprouts
What are Extra-intestinal pathogenic E Coli? What causes the diease?
Strains of E Coli capable of causing disease outside the intestinal tract
Wide range of virulence factors: Adhesion, iron acquisition systems, protectin and invasins, toxins and others etc…
How do urinary tract infections occur?
Uropathogenic E Coli transfer from the rectum to the urethra and then migrate to the bladder causing cystitis
Occurs more frequently in women as its closer
Often self-limiting e.g. not treated will probably go away
However can cause further complications
How do the virulence factors lead to UTIs (cystitis)?
Adhesion
–> Type 1 fimbriae–> adhesive tips attach to alpha-D-mannosylated proteins on uroepithelium–> mediates adhesion, invasion and formation of intracellular bacterial communities
Toxin
–> LPS
–> Alpha-haemolysin–> pore forming toxin, cytotoxic towards epithelial cells
Iron acquisition
–> Avaliability of iron is restricted
–> Bacteria produce their own iron-complexing proteins (siderophores) to acquire iron
What can happen if UTI are not treated?
Can lead to cause kidney infection
Bloodstream infections
Whats is significant about E Coli and bloodstream infections?
Commonest cause of bloodstream infection
High mortality rates–> 2016/17–> 14.8% 30 day all-cause mortality
