L8: V. cholerae & C. diff Flashcards
Cholera is a __ disease
water-borne
What percentage of cholera cases can be successfully treated with oral rehydration salts?
up to 80%
Which two serogroups of V. cholerae cause outbreaks?
O1 (majority) and O139
Features of V. cholerae
- Gram negative
- Motile, curved rod with a single polar flagellum
- Produces a complex A-B toxin
How is V. cholerae transmitted?
via the oral route: consumption of contaminated water
How many serogroups are known?
200
2 subgroups of serogroup O1
Classical and El Tor
Symptoms of cholera
large amounts (loss of ~20L water/day) of diffuse watery diarrhoea (‘rice water stool’), vomiting, muscle cramps, circulatory collapse in serious cases
Survival of acute diarrheal disease (cholera) leads to…
recovery with immunity - some potential to carry and shed the pathogen
Features of O1 El Tor strain
haemolytic, polymyxin B resistant
First line treatment for cholera
Oral or intravenous hydration - prompt restoration of lost fluids and salts
What antibiotic is recommended as first line treatment for adults, in conjunction with hydration?
Doxycycline - inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit
What is required for successful colonisation of the gut by V. cholerae?
motility - to penetrate the mucus barrier to adhere to SI mucosal surface
V. cholerae preferentially colonises the __ __ __, forming microcolonies in __ __.
distal small intestine
villous crypts
How is the mucosal barrier disrupted?
- Widening of intracellular spaces
- Disruption of the apical junction
What type of toxin does V. cholerae produce?
Hexametric cholera enterotoxin, which is composed of 1A chain and 5B chains
Which part of the toxin is the toxic component?
The A chain (ADP-ribosylase)
Toxin binds to __ on the surface of intestinal epithelial cells.
GM1 ganglioside receptor
What immune cells are involved in disrupting the mucosal barrier in cholera infection?
Influx of neutrophils, macrophages, APCs & other lymphocytes into lamina propria. Cholera also triggers the production of innate effector molecules at the mucosal surface, such as lactoferrin, defensins & oxidases.
Which proteins generate ROS in cholera infection?
dual oxidase 2 (DUOX2), inducible nitric oxide synthase (iNOS)
Which signalling pathways are highly activated in response to cholera?
NLRP3 inflammasome and Type I IFN
Which cytokines are produced by APCs in cholera infection?
IL-1β (pro), IL-6 (pro/anti), IL-17 (pro)
Protection against cholera infection is delivered by
V. cholerae specific IgA antibodies
What is the primary virulence factor of V. cholerae?
Enterotoxin production
What is a requirement of live attenuated (recombinant) vaccines?
No virulent forms present in inoculum
Inactivated __ is not effective as a vaccine.
enterotoxin
2 examples of vaccines for people travelling developed by PaxVax Corporation
PXVX0200 (Vaxchora): single-dose, oral, live attenuated vaccine against cholera
PXVX0103: oral, live adenoviral-based vaccine against Avian Influenza (H5N1)
What strain in Vaxchora is well-tolerated and protects against cholera?
CVD 103-HgR
Features of Clostridium difficile
- Gram positive
- Spore-forming
- Anaerobic bacillus
How is C. diff transmitted?
via the faecal-oral route
How does C. diff cause infection?
by colonising the LI, when normal flora is reduced by antibiotics
- generally nosocomial
Risk factors associated with CDI
- higher risk after antimicrobial therapy
- patients over 65 years
CDI can affect any part of the colon but __ __ is most commonly affected.
distal segment
Main protective barrier against CDI
normal intestinal microflora
C. diff infection can result in…
pseudomembranous colitis (potentially fatal) or antibiotic-associated diarrhoea
What play an important role in the induction of C. diff spore germination?
bile acids
__ __ concentrations appear to be higher in faeces of patients with CDI.
primary bile (cholic acid)
__ __ concentrations appear to be higher in faeces of healthy people.
secondary bile (deoxycholic acid)
Is C. diff invasive?
No
C. diff virulence is caused mainly by
enzymes such as collagenase and hyaluronidase, as well as toxins
C. diff virulence leads to
- damage in epithelial cell cytoskeleton
- disruption of tight junctions → fluid secretion
- neutrophil adhesion → local inflammation
(leading to breakdown of gut barrier integrity, & loss of functionality)
C. diff toxins
Toxin A (an entertoxin) and toxin B (a cytotoxin)
What effect do C. diff toxins have?
They are transported to cell cytoplasm & activate the Rho family of GTPases
- inactivate G protein
- impair actin-polymerisation
- cytoskeletal disorganisation & loss of cell function
~6% of C. diff strains produce a __ __.
binary toxin (an extra toxin)
What feature does C. diff 027 strain have?
a frameshift stop codon in the tcdC negative regulator (hyper-expresses the A & B toxins)
027 strain has increased sporulation rate
All C. diff 027 strain isolates are positive for what?
the binary toxin
027 strain of C. diff is resistant to?
fluoroquinolones
How is CDI diagnosed?
by detection of toxin in stools of patients by ELISA assays
What is used in C. diff culturing?
cycloserine-cefoxitin fructose agar (CCFA)
What antibiotics are recommended for C. diff treatment?
Vancomycin
Fidaxomicin
Restrict specific antibiotics, especially __ and __, in elderly population for C. diff control.
Cephalosporins and Clindamycin
Name 2 potential new therapies under trial for CDI
- probiotics
- FMT
Human monoclonal antibody against the C. diff toxin B?
Bezlotoxumab (Zinplava)
- has been shown to reduce the risk of recurrent CDI in those at high risk of recurrence
- inhibits the binding of toxin B & prevents its effects on mammalian cells
