E. coli Flashcards
1
Q
Describing E coli
A
- Gram negative rods (red stain)
- Lactose- fermenting
- Facultatively anaerobic- large bowel
- Often motile
- Numerous serotype
- Causes different types of diseases
- Constituent part of large bowel microbiota of many animals inc. humans
- In other animals too
2
Q
Complex ecology of E. coli- ‘ One health’ ecology approach
A
- Transmission of E coli between animals, humans and the environment, including pathogenic and antibiotic resistant strains
- Illustrates the challenges of controlling disease and the spread of resistance
3
Q
E coli under the microscope
A
4
Q
gram stain results
A
gram negative rods
5
Q
Identifying E coli in the laboratories
A
- E.coli and other Enterobacteriaceae can use the sugar lactose as an energy source à producing lactic acid as a waste product
- MacConkey agar contains lactose and a pH indicators that goes red with acid pH
- E coli and other Enterobacteriaceae grow as pink colonies
- Non lactose fermenters grow as yellow colonies
6
Q
antigens found on E.coli
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- O
- H
- K
- F antigens
7
Q
E.coli can ve indentified by
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- serology using antibodis to detect bacterial surface antigens
- metabolic profiling variation in biochemical pathways
genomic divery
8
Q
serological antigens of E.coli
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- PAMPs
- Body can recognise PAMPS e.g. LPS, flagella, cell membrane, fimbriae and capsule
- Different strains of E.coli will have different molecular patterns of LPS- may not be recognised
9
Q
Genetic diversity of E.coli
A
1509 E coli strains isolated from blood cultures and examined by whole genome sequencing
- Overall there are over 70,000 genes identified in all isolates, but only 885 genes present in all 1509 isolates
10
Q
E.coli in health and disease
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- Normal part of large bowel microbiota in humans and many other animals
- Possibly protects against invasion by pathogenic species such as Salmonella
11
Q
diseases caused by e.coli
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- Intestinal infections (diarrhoea)
- Toxin-mediated disease
- Extra-intestinal infections
- UTI
- Intra-abdominal
- Biliary tract
- Bloodstream infection
- Neonatal meningitis
12
Q
E.coli diarrhoea
A
6 pathotypes of diarrhoeagenic E coli
- EPEC and EIEC are most common amount young children in developing world
- EAggEC re most common among immunocompromised persons
13
Q
Enterotoxigenic E coli (ETEC)
A
- Important cause of bacterial diarrhoeal illness
- Major cause of diarrhoea in lower-income countries- especially among children
- Leading cause of travellers diarrhoea
- Faeco-oral transmission
- Onset is 1-3 days after exposure and usually lasts 3-4 days
14
Q
ETEC virulence factors
A
Produces 2 toxins
- Heat stable toxin (ST)
- Heat- labile toxin (LT
- Illness cause by each toxin is similar
- They stimulate the lining of the intestine causing them to secrete excessive fluid producing watery diarrhoea and abdominal cramping
15
Q
less common side effects of ETEC
A
- Fever
- Nausea
- Vomiting
- Chills
- Loss of appetite
- Headache
- Muscle ache
- bloating
16
Q
Enteropathogenic E coli (EPEC)
- Causes the localised effacement of microvilli and intimately attaches to the host cell surface, forming characteristic attaching and effacing (A E) lesions
- Intimate attachment requires the type III-mediated secretion of bacterial proteins, several of which are translocated directly into infected cells, including the bacteria’s own receptor (Tir)
- Binding to this membrane bound, pathogen-derived protein permits EPC to intimately attach to mammalian cells
- The translocate EPEC proteins also activate signalling pathways within the underlying cells- reorganisation of the host actin cytoskeleton and the formation of pedestal-like structures beneath the adherent bacteria
Insertion of transloacted intimin receptor Tir) into enterocyte cell membrane and binding to intima
A
17
Q
Shiga toxin-producing Ecoli (STEC)
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- First outbreak reported in 1982
- Causes haemorrhagic colitis (bloody diarrhoea) and haemolytic uremic syndrome (HUS- triad of acute renal failure, haemolytic anaemia and thrombocytopenia)
18
Q
symptoms and signs of Shiga toxin-producing Ecoli (STEC)
A
- Severe crampy abdominal pain
- Initially watery diarrhea
- Followed by grossly bloody diarrhea
- Little or no fever
19
Q
Molecular action of Shiga toxin
A
- B sub-units of shiga toxin binds to Gb3 on host cell surface
- After binding, the toxin is endocytosed and transported to the goli apparatus and endoplasmic reticulum
- During the intracellular transport the A chain is cleaved into the small A2 fragment and the enzymatically active A1 fragment
- A fragments are kept together by a disulphide bond until the toxin reaches the ER, where the A1 fragment is released and translocated into the cytosol
- In the cytosol, the A1 part inactivates ribosomes thereby inhibiting protein synthesis, eventually resulting in death
20
Q
what are extra-intestinal pathogenic E.coli (ExPEC)
A
- Strains of E coli capable of causing disease outside the intestinal tract
e. g. E coli urinary tract infections
e. g. E coli bloodstream infections
21
Q
virulence factors of ExPEC
A
- Adhesins
- Iron acquisition system
- Protectins and invasins
- Toxins
- Others
22
Q
Genesis of urinary tract infections
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- Very common women but unusual in men
- Difference explained by anatomical differences between women and men
- Uropathogenic E coli transfer from the rectum to the urethra and then migrate to the bladder causing cystitis
23
Q
cystis risk factor
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- femal sex, history of UTI
- sexual acitvity
- vaginal infection
- diabetes, obesity, genetic susceptibility
24
Q
clinical symptoms of cystisis
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- frequent and urgent urination
- dysuria
- nocturia, hematuria, malaise
25
causative organisms of cystitis
* UPEC
* Klebsiella pneumoniae
* Staphylococcus saprophyticus
* Enterococcus faecalis
26
UPEC virulence factor for cystisis
Adhesins (Type 1 and othe chaperone- usher pili)
Toxins (HlyA, CNF1)
Siderphores
Capsule
27
risk factors of pyelonephritis
diabetes
HIV/AIDs
iatrogenic immunosuppression
COngenital or acquire urodynamic abnormalities
28
clinical symptoms of pyelonephirtis
- back pain
- fever, chills, malaise
- nausea, vomiting, anorexia
29
pyelonephritis causative organisms
* UPEC
* Klebsiella pneumonoa
* S. aureus
* Enterococcus aureus
* Enterococcus faecalis
* Proteus spp
30
selected UPEC VF of pyelonephritis
* adhesins (Type 1 and P pilli)
* Toxins (HIyA, CND A)
* Siderphores
* Flagella
31
adhesins
* Type 1 fimbriae have adhesive tips that bin to alpha-D -mannosylated proteins on uroepithelium and the formation of intracellular bacterial communities (IBCs)
32
Toxins
* LPS
* Alpha-haemolysins (HlyA) is a secreted, pore-forming toxin, cytotoxic towards epithelial cells in the UT
33
UPEC iron acquisition
* Availability of iron is extremely restricted in the UT
* Bacteria produce their own iron-complexing proteins (siderphores) to acquire iron
34
E. coli bloodstream infections
* E coli bacteria are the commonest cause of bacterial bloodstream infection in England and the number of infections is rising
* Around half of E coli bloodstream infections occur in patients older than 75 years
* Causal factors
* 50% UTIs- linked to ineffective antibiotic treatment
* 21% of patients have urinary catheters
* 16% hepatobiliary infections
* 7% GI infections
35
Prevention of E.coli infections- diarrhoea
* Avoid foods and drink that could contaminated with bacteria
* Raw fruits and vegetables (e.g. salads), raw seafood or undercooked meat or poultry, unpasteurised dairy products, food from street vendors, and untreated water (inc ice) in areas lacking adequate chlorination
36
Treatment of E.coli- diarrhoea
* Mostly infected persons will recover within a few days without requiring specific treatment
* Clear liquids are recommended for persons with diarrheal to prevent dehydration and loss of electrolytes
* Oral rehydration solutions
* Avoid antibiotics- may make illness worse
37
treatment for UTIs caused by E.coli infection
* Commonly used: trimethoprim and nitrofurantoin
* 60% of E coli tested in labs is trimethoprim resistant
* Increasing resistance to a wide range of antibiotic classes
* Horizontal transfer of resistance
