ICL 2.21: Helicobacter, Campylobacter & Vibrio Flashcards
what is the causitive agent of gastric ulcers?
helicobacter pylori
what did people used to think caused gastric ulcers?
Excess acid, smoking, stress, spicy foods
these are now recognized as AGGRAVATING, not causal, factors
what is the microbiology of helicobacter pylori?
gram (-) helical rods
microaerophilic = tiny little bit of oxygen
are helicobacter pylori motile??
yes
tufts of several polar flagella (4-7)
highly motile!!
corkscrew motility like spirochetes but different mechanism
how is helicobacter pylori transmitted?
fecal-oral and oral-oral
is carriage with helicobacter pylori common?
incidence of carraige in developing countries is high
it’s lower in developed countries
how does H. pylori enter into the acidic stomach?
the stomach lumen is really acidic so it’s a pretty hostile environment so H. pylori overcomes this by:
- production of urease which converts urea to NH3 + CO2
NH3 raises the pH in the immediate vicinity of the bacteria and acts a buffer
- flagella
H. pylori is highly motile, can quickly reach the mucin layer
the mucin layer is mostly negatively-charged sulfated polysaccharides, acts as buffer to protect gastric epithelial cells – it has a neutral pH 7
what mechanisms does H. pylor use to reach the gastric epithelium from the lumen of the stomach?
so the problem is that the mucus in the mucin layer of the stomach is really thick and viscous and hard to get through so to overcome this H. pylori:
- has flagella which confer corkscrew motility on the helical cells
- express mucinase and phospholipases to liquify the mucus
how does H. pylori colonize the gastric epithelium?
so the problem is that stomach contents flow through the GI system so H. pylori colonizes the gastric epithelium by:
- expression of adhesins like:
BabA which binds Lewis b Ag
SabA which binds sialyl Lewis X
HpaA which binds neuraminyl-lactose
how does H. pylori evade the immune system?
- catalase, arginase and superoxide dismutase detoxify ROS produced by immune cells
- H. pylori LPS not very toxic or immuno-genic, looks like “self” (carbohydrates identical to Lewis antigens x and y)
- H. pylori flagellin is poorly recognized by TLR5
- VacA protein inhibits T cell proliferation, interferes with B-cell Ag presentation.
how does H. pylori cause damage?
- ammonia produced by urease damages host cells
- cytotoxin VacA causes influx of cations in vacuoles – gastric cells swell and die; also loosens junctions between epithelial cells
- colonization itself may elicit inflammatory response, with infiltration of submucosal tissues by immune cells
- NAP (neutrophil activation protein) activates immune cells to produce ROI
- CagA phosphorylates host proteins, promoting activation of NF-kB and production of IL-8 (crucial determinants of chronic inflammation)
what serious illness is H. pylori linked to?
gastric cancer
H. pylori has mutagenic properties that trigger DNA ds-breaks and DNA damage which leads to cancer!
CagA (+) strains are particularly associated with cancer risk
how does H. pylori cause gastric cancer?
- colonization of stomach by H. pylori
- after a few weeks/months the bacteria causes chronic superficial gastritis
- then you can get either:
- chronic atrophic gastritis –> gastric adenocarcinoma –> proliferation in the prescence of ROS and RNS results in DNA damage and mutation
- lympoproliferative disease –> B cell MALT lymphoma
- peptic ulcer disease
how do you diagnose H. pylori?
- silver stain of gastric epithelial cells = small curved rods associated with the surface of gastric epithelial cells
- urease test/staining/culture of biopsy = invasive
- serologic test, urea breath test = non-invasive
- culture/PCR
how do you culture H. pylori?
3 days for isolated colonies to appear, under reduced O2 / increased CO2 @ 37oC on BAP (blood agar plate)
how do you treat H. pylori?
NIH recommends that all patients with gastric or duodenal ulcers caused by H. pylori be treated with antimicrobials
but with the antibiotics you need to include a proton-pump inhibitor!!!
this is because PPIs don’t work well at low pH aka the stomach
but if someone has an asymptomatic H. pylori infection you actually shouldn’t treat them because it appears to offer protection from gastroesophageal reflux disease and adenocarcinomas of the lower esophagus and gastric cardia
what are the key virulence factors of H. pylori?
- flagella
motility, immune evasion because not seen by TLR5
- urease
resistance to acidic environment of the stomach
- LPS
low toxicity and immunogenicity
- adhesins
allow retention on gastric mucosa
what’s the microbiology of campylobacter?
gram (-) spiral shaped rods
urease negative
what disease state does campylobacter jejuni cause?
1 (or #2) cause of bacterial gastroenteritis in US
it’s either this or salmonella depending on who you ask
what are the symptoms of a campylobacter jejuni infection?
- fever
- abdominal pain that can mimic appendicitis
- diarrhea (often bloody)
symptoms are self-limiting; only last a week
how is campylobacter jejuni transmitted?
transmission via contaminated food, milk, water
especially chicken
person-person spread is rare
what is the pathogenesis of campylobacter jejuni?
damages mucosal surfaces of the jejunum and colon
mucosal surface appears ulcerated and bloody
there’s also cryptic abcesses in epithelial glands and infiltration of lamina propria with neutrophils, monocytes and eosinophils
however the virulence factors are poorly defined
what toxin is associated with C. jejuni?
cytolethal distending toxin (CDT)
it delivers DNAse (CdtB) to host cell, blocking mitosis and in some cells triggering apoptosis
it has DNAse activity
it induces cell cycle arrest and death in intestinal and T-cells
induces production of IL8
what are the important virulence factors of C. jejuni?
- capsule = immune vasion
- invasion factors = immune evasion, tissue damage
- adhesins = adherence to mucus and gastric cells
- toxin = CDT
- flagellum = motility, poorly recognized by TLR5
- LOS
what is Guillain-Barre syndrome and which bacteria is it associated with?
C. jejuni
can be triggered by other bacteria as well (Haemophilus influenzae, Mycoplasma pneumoniae) and some viruses
causes paralysis which can last for several weeks
this is due to demylination of nerves because of autoimmune syndrome
this autoimmune response happens because the C. jejuni LOS looks identical to myelin gangliosides to out antibodies start attacking our nerves
how do you treat Guillain-Barre syndrome?
plasma exchange
respirator if necessary
corticosteroids
how do you diagnose C. jejuni infection?
- gram stain = thin, spiral shaped pink rods
- ELISA for campylocater common antigen
- culture from stool sample
in what conditions is C. jejuni cultured?
takes 2-3 days for isolated colonies to appear
they need reduced O2 and increased CO2
42 C on selective medium –> 42 C is the body temperature of a chicken
how do you differentiate H. pylori vs. C. jejuni?
H. pylori = urease (+), has several flagella and grows at 37 C
C. jejuni = urease (-), 1 flagella, grows at 42 C
FLASHCARD: C. jejuni
1/2 cause of bacterial gastroenteritis
small, gram (-) curved rod
fastidious, microaerophilic
resembles h. pylori BUT only has 0-1 flagella, grows at 42 C, and is urease negative
zoonosis = contaminated food, unpasteurized milk, contaminated water
can cause the autoimmune disease Guillain-Barré Syndrome = paralysis because C. jejuni LOS resembles carbohydrates on surface of nerve cells
virulence factors are not well characterized –> produces a DNase toxin (CDT)
what pathogen caused this?
overall good health presents with abdominal discomfort and diarrhea
for preceding 2d, intermittent, crampy periumbilical abdominal pain
For preceding week, mild abdominal discomfort and 3 loose bowel movements/day
Denied: drinking well water, having fever, blood in stool, recent antibiotic use, relation of pain to meals, dysuria or hematuria
remembered eating chicken at a banquet over a week earlier
stool sample contained white blood cells
C. jejuni
what pathogen caused this?
kid brought to ED in Haitii because 10 h vomiting and diarrhea
Admitted; shared a cot with a pediatric patient who had similar symptoms
BP and temp were not obtained (lack of equipment), but did not feel warm
Skin recoil was less than 1 second but not instantaneous = dehydrated
mild abdominal tenderness
Stool sample was translucent fluid with small flecks of mucus = “rice water” appearance –> no feces, no blood, no WBCs
Culture of stool sample yielded Gram-negative, comma-shaped bacteria after 24 h growth (result obtained 1 wk later)
Patient fully recovered after 4 d rehydration therapy – also treated with azithromycin to reduce risk of spread
vibrio cholerae
what’s the microbiology of vibrio cholerae?
comma-shaped gram (-) rod
facultative anaerobe
is vibrio cholerae motile?
yes
single-long polar flagellum
how do you acquire a vibrio cholerae infection?
ingestion of contaminated water, food or improperly cooked seafood (shellfish)
John Snow did the well experiment and realized it was coming from a specific well = contaminated water
what is the clinical presentation of vibrio cholera?
abrupt onset of watery diarrhea and vomiting –> 1L/hr!!!!
stools are rice water and loaded with mucus
severe dehydration; skin loses plasticity
metabolic acidosis
hypokalemia = loss of K+
hypovolemic shock
cardiac arrhythmia, kidney failure
what is the mortality rate of V. cholerae?
60% if not treated within HOURS
<1% if treated though
does V. cholerae cause disease via immune response or toxins?
it’s a toxin-mediated disease!!!
the toxin is specified by ctxAB genes –> if there isn’t this gene to code for the toxin then there’s no diarrhea!
ctxAB genes are expressed by the O1 and O139 serotypes
what type of toxin does V. cholerae have? how does it work?
Ctx is a A-B type exotoxin
B binds to ganglioside GM1 on surface of intestinal cells
then A is internalized and ADP-ribosylates Gsα protein
normally Gsα is a GTP-hydrolyzing protein that regulates host adenylate cyclase and therefore cAMP levels
but ADP-ribosylation of Gsα by Ctx locks it in the “ON” phase, so host adenylate cyclase always produces cAMP
this leads to hypersecretion of water and electrolytes (Cl-, Na+, HCO3-)
what are the steps in the patholgenesis of V. cholerae?
- ingestion
- goes through stomach rapidly using its flagellum
- adheres to and colonizes small intestine using several adhesins
- production of toxins = Ctx, Zot, Ace
- extensive fluid and ion loss from tissues leading to hypotension, electrolyte imbalance and death
what is the size of the inoculum required to get a V. cholera infection?
ID50 is really big….
size of inoculum is crucial because bacterium is acid-sensitive
how do you treat V. cholerae infections?
rehydration and electrolytes are essential and urgently needed
antibiotics are often used to shorten the course of the disease and reduce spread, but are not required
what kind of diarrhea is associated with vibrio cholerae?
secretory diarrhea = copious watery stool
no blood or WBCs
what kind of diarrhea is associated with campylobacter?
dysentery = low volume, blood mucus +/- WBCs
what are the clinical symptoms of Ctx+ V. cholerae?
abrupt onset of watery diarrhea, can progress to severe dehydration, metabolic acidosis, hypokalemia, hypovolemic shock
what are the clinical symptoms of Ctx- V. cholerae?
Gastroenteritis, milder form of watery diarrhea
what are the symptoms of V. parahaemolyticus?
1 US cause of seafood-associated gastroenteritis = raw oysters!
Explosive onset of watery diarrhea within 24 h of exposure (not as high volume as cholera)
Nausea, vomiting
Abdominal cramps
Headache and low grade fever
self limiting = 3 days
treatment = rehydration
what are the virulence factors for V. paraheomolyticus?
- hemolysin
- flagellum
- capsule
- other exotoxins
what are the symptoms of a V. vulnificus infection?
1 cause of seafood-related US deaths
symptoms after ingestion in otherwise-healthy patients:
- diarrhea
- nausea
- vomiting
- abdominal cramps
in immunocompromised patients:
- bacteremia
- fever/chills
- low BP = shock
- blistering skin lesions (vulnificus!)
in BOTH healthy and immunocompromised patients it’ll cause necrotizing fasciitis if it enters a wound
what are the virulence factors of V. vulnificus?
- capsule = antiphaogcytic, complement resistance
- cytolysin/hemolysin = tissue damage
- metalloprotease
- siderophores
- RtxA toxin
- flagellum
- pilus
what are the 3 main vibrio species that cause gastroenteritis?
- V. parahaemolyticus
- V. volnificus
- V. cholerae
O1 and O139 serotypes are Ctx+ and cause cholera – other serotypes are Ctx– and cause gastroenteritis
are vibrio infections toxin or immune mediated diseases?
toxins are mainly responsible for clinical manifestations
