Dr. Jumana Abbadi

Vibrios, Campylobacters,

Helicobacters (Curved rods)

Chapter 32p.265-577

Introduction

Curved Gram-negative rods includes:

Vibrio cholera, the cause of cholera.

Helicobacter pylori, the cause of gastritis and gastric ulcer disease.

Campylobacter jejuni, one of the most common causes of

diarrhea.

Vibrio species

Vibrios are curved, Gram-negative rods.

Commonly found in saltwater.

They are highly motile with a single polar flagellum,

Non–spore-forming.

Oxidase positive.

They can grow under aerobic or anaerobic

conditions, i.e. facultative anaerobes..

There are many species:

V. cholera

V. mimicus

V. parahemolyticus; causes gastroenteritis

V. vulnificus.

Vibrio Cholera

Vibrio cholera has a low tolerance for acid, but grows under

alkaline (pH 8.0-9.5) conditions.

It is distinguished from other vibrios by biochemical

reactions, lipopolysaccharide (LPS) O antigenic structure,

and production of cholera toxin (CT).

In aquatic environments, V. cholera produces polysaccharide

biofilms, which contain carbohydrate moieties mediating

cell–cell adhesion and attachment to surfaces.

There are over 200 O antigen serotypes, only two of which

produce cholera toxin causing endemic and/or epidemic

cholera:

O1

O139

Non-O1 and non-O139 strains and they cause mild cholera-

like diarrhea. Non-O1 and non-O139 strains have been

sporadically isolated from cases of gastroenteritis but do not

produce CT, and thus not the disease cholera.

Epidemiology

It has a short incubation period (2 days).

Epidemic cholera is spread primarily by contaminated water

under conditions of poor sanitation, particularly where

sewage treatment is absent or defective.

Cholera is currently endemic in the Indian subcontinent,

Africa and inYemen.

The epidemic potential of V. cholera depends on its ability to

survive in both aquatic environments and human hosts.

The organism is fragile, surviving only a few days in the

environment outside its human hosts.

Virulence Factors

1. Motility by flagella: V. cholera must swim to the small

intestine, multiply, and produce virulence factors.

2. Adherence to the epithelial cells by pili: which leads to

colonization of the entire intestinal tract.

3. Cholera Toxin: the outstanding feature of V. cholera

pathogenicity is the ability of virulent strains to secrete CT.

Pathogenesis: Cholera toxin CT is an A-B type ADP-ribosylating

toxin.

Its molecule is an aggregate ofmultiple polypeptide chainsorganized into two toxic subunits(A1,A2) and five binding (B) units.

The B units bind to a GM1-ganglioside receptor found on thesurface of many types of cells. Oncebound, the A1 subunit is released fromthe toxin molecule, and it enters thecell by translocation.

In the cell, The toxic A1

subunit catalyzes the ADP-

ribosylation of the GS

(stimulatory) regulatory

protein, “locking” it in the

active state.

Because the GS protein

activates adenylate cyclase

(AC). The net effect is

persistent activation of

adenylate cyclase.

The increased adenylate cyclase

(AC) activity results in

accumulation of cAMP along the

cell membrane.

This in turn leads to

hypersecretion of chloride,

potassium, bicarbonate,

and associated water

molecules out of the cell

into the intestinal lumen.

The result is dehydration (isotonic fluid loss), hypokalemia

(potassium loss), and metabolic acidosis (bicarbonate loss).

The intestinal mucosa remains unaltered except for some

hyperemia, because V. cholera does not invade or otherwise

injure the enterocyte.

Disease Manifestations Rapid onset, beginning

with abdominal fullnessand discomfort, rushes ofperistalsis, and loose stools.

The stools quickly becomewatery, voluminous, almostodorless, and containmucus flecks (rice-waterstools).

Neither white blood cellsnor blood are in the stools,and the patient is afebrile.

Clinical features of cholera result from the extensive fluid

loss and electrolyte imbalance, which can lead to extreme

dehydration, hypotension, and death within hours if

untreated.

No other disease produces dehydration as rapidly as cholera.

DIAGNOSIS

The initial suspicion of cholera which depends on the typical

clinical features of the diarrhea (rice-water stools).

A bacteriologic diagnosis is accomplished by isolation of V.

cholera from the stool.

The organism grows on common clinical laboratory media

such as blood agar and MacConkey agar, but its isolation is

enhanced by a selective medium thiosulfate–citrate–bile

salt–sucrose agar (TCBS).

V. cholera is oxidase positive.

Tretment The outcome of cholera depends on balancing the diarrheal

fluid and ionic losses with adequate fluid and electrolytereplacement (oral or intravenous).

Oral replacement, particularly if begun early, is sufficientfor all but the most severe cases and has substantially reducedthe mortality from cholera.

Antimicrobial therapy plays a secondary role to fluidreplacement by shortening the duration of diarrhea.

A single dose of azithromycin provides optimal therapy

doxycycline, a fluoroquinolone, or trimethoprim-sulfamethoxazole are also effective agents.

Prevention

Boiling and chlorination of water during epidemics are required.

Cholera associated with ingestion of crabs and shrimp can be

prevented by adequate cooking (10 minutes) and avoidance of

recontamination from containers and surfaces.

Campylobacter species

Motile, curved, oxidase-positive, Gram-negative rods

The cells have polar flagella and are often attached at their

ends giving pairs “S” shapes or a “seagull” appearance.

C. jejuni is by far the most common prototype for intestinal

disease.

Camplybacter jejuni

It is one of the most common causes of infectious

diarrhea.

Like other campylobacters, C. jejuni grows well only on

enriched media under microaerophilic conditions. That

is, it requires oxygen at reduced tension (5%-10%),

presumably because of the vulnerability of some of its

enzyme systems to superoxides.

Growth usually requires 2 to 4 days, sometimes as much as 1

week.

Virulence Factors

Polar flagellum; the cells are actively motile.

It produces a membrane-bound protein called cytolethal

distending toxin (CDT).

Epidemiology

It is the leading cause of gastrointestinal infection in

developed countries followed by Salmonella species.

This high rate of disease is facilitated by the low infecting

dose of C. jejuni; only a few hundred cells are enough to cause

and infection.

Campylobacters are commonly found in the normal

gastrointestinal and genitourinary flora of warm-blooded

animals, including sheep, cattle, chickens, wild birds,

and many others.

The most common source of human infection is undercooked

poultry, but outbreaks have been caused by contaminated

rural water supplies and unpasteurized milk often consumed

as a “natural” food.

Pathogenesis Infection is established by oral

ingestion, followed bycolonization of the intestinalmucosa.

Adherence to enterocytes isfacilitated by action of theflagellum followed by entranceinto cells in endocytotic vacuoles.

injury mechanisms include thecytotoxic CDT. CDT has an A-B toxin structure in which the Asubunit is able to cause cell cyclearrest.

The intestinal pathology is that of an invasive pathogen with

acute inflammation, crypt abscesses, and occasional

seeding of the bloodstream.

There is an association between C. jejuni infection and

Guillain-Barré syndrome, an acute demyelinating

neuropathy that is frequently preceded by an infection.

Up to 40% of patients have culture or serologic evidence of

Campylobacter infection at the time the neurologic symptoms

occur.

Disease Manifestations

The illness typically begins 1 to 7 days after ingestion, with

fever and severe lower abdominal pain.

These are followed within hours by dysenteric stools that

usually contain blood and pus.

The illness is typically self limiting after 3 to 5 days but may

last 1 to 2 weeks.

Diagnoses

The diagnosis is confirmed by isolation of the organism from

the stool.

This requires a special medium made selective for

Campylobacter species; Campy-agar. The plates must be

incubated in microaerophilic atmosphere

Treatment

Patients are usually not treated unless the disease is severe

or prolonged (lasting longer than 1 week).

Erythromycin or azithromycin is considered the

treatment of choice but must be given early for maximal

effect.

Helicobacter It was well known for physicians that the cause of peptic ulcer was

an imbalance between gastric acid–pepsin secretion and an

underlying genetic and lifestyle background (smoking, anxiety,

stress).

In 1983, a pair of Australian microbiologists (Warren and

Marshall) suggested that gastritis and peptic ulcers were

infectious diseases. With time it became established that

Helicobacter pylori is the cause of peptic ulcer and treatment

with antibiotics resolved the disease.

Helicobacter pylori

The cells are slender, curved Gram-negative rods with

multiple polar flagella (rapidly motile).

Growth is slow (3–5 days) and requires a microaerophilic

atmosphere.

Virulence Factors

Urease:

Whose action allows the organism to persist in low pH environments

(stomach) by the generation of ammonia.

Vacuolating cytotoxin (VacA):

A secreted protein which causes apoptosis in eukaryotic cells.

CagA (Cytotoxin-associated gene A) protein:

induces changes in multiple cellular proteins and has a strong

association with virulence.

Injection secretion systems (type IV):

Which delivers bothVacA and CagA into cells.

Epidemiology

Infection with H. pylori causes what is perhaps the most

prevalent disease in the world.

The organism is found in the stomachs of 30% to 50% of

adults in developed countries, and it is almost universal in

developing countries.

The exact mode of transmission is not known, but is

presumed to be person to person by:

fecal–oral route or

gastric secretions

Colonization increases progressively with age.

Helicobacter pylori is the most common cause of gastritis,

gastric ulcer, and duodenal ulcer cases which are not

due to drugs.

H. pylori gastritis may progress into gastric

adenocarcinoma especially in strains that are positive for

cytotoxin-associated gene A (Cag A).

It is also linked to a gastric mucosa-associated

lymphoid tissue (MALT) lymphoma.

Pathogenesis To persist in the stomach, H.

pylori uses many mechanisms toadhere to the gastric mucosa andsurvive the acidic environmentof the stomach. The flagella allows the

organisms to swim to the lessacidic locale beneath the gastricmucin layer.

The urease further creates amore neutral microenvironmentby ammonia production.

At the mucosa, adherence ismediated by multiple outermembrane proteins which bindto the surface of gastricepithelial cells.

The inflammation may be due totoxic effects of the VacAtransported into the gastricepithelial cells by the secretionsystem. The VacA directlyinduces cellular changes(vacuolization) and death.

The CagA protein is injectedinto the gastric epithelial cell bythe secretion system, whereit triggers multiple enzymaticreactions including those thatcause reorganization of the actincytoskeleton and stimulation ofcytokines.

Helicobacter pylori colonization

and inflammation is always

accompanied by a cellular

infiltrate ranging from minimal

mononuclear infiltration of the

lamina propria to extensive

inflammation with neutrophils,

lymphocytes, and microabscess

formation.

This prolonged and aggressive inflammatory response could

lead to epithelial cell death and ulcers.

After decades, this inflammation and assault by the virulence

factors just described could cause metaplasia, and

eventually cancer.

Disease Manifestations Primary infection with H. pylori is either silent or causes an

illness with nausea and upper abdominal pain lasting up to 2weeks.

Later, the findings of gastritis and peptic ulcer diseaseinclude nausea, anorexia, vomiting, epigastric pain.

Many patients are asymptomatic for decades, even up toperforation of an ulcer. Perforation can lead to extensivebleeding and peritonitis due to the leakage of gastric contentsinto the peritoneal cavity.

Diagnosis1. The most sensitive means of diagnosis is endoscopic

examination, with biopsy and culture of the gastricmucosa.

2. Serology:

Detection of antibodies (IgG, IgA) directed against H. pylori.Because IgG or IgA remains elevated as long as the infectionpersists, these tests are valuable both for screening and forevaluation of therapy.

3. Urea breath test:

the patient ingests 13C- or 14C-labeled urea, from which theurease in the stomach produces products that appear as labeledCO2 in the breath.

Urea breath test

Treatment

Cure rates approaching 90% have been achieved with various

combinations of bismuth salts and/or a protein pump

inhibitor plus two antibiotics for at least 2 weeks

Antibiotics:

Clarithromycin plus amoxicillin or metronidazole.

OR

metronidazole plus tetracycline.

Vibrio cholera Campylobacter jejuni Hellicobacter pylori

curved curved curved

Saltwater Animals Humans, gastric secretions

Single flagellum Single flagellum Multiple polar flagella

Oxidase positive Oxidase positive Oxidase positiveUrease positive

Facultative anaerobes Microaerophilic Microaerophilic

Low tolerance for acid Medium tolerance to acid High tolerance for acid

Rice-water diarrhea Diarrhea; dysentery Peptic ulcer and gastritis

Large infection dose Low infecting dose

Cholera toxin Cytolethal distending toxin (CDT) • Vacuolating cytotoxin (VacA)• Cytotoxin-associated gene A (CagA)

Acute Acute Chronic

Diagnosis by culture:• Blood agar• MacConkey agar• Thiosulfate citrate bile

salt sucrose agar

Diagnosis:Culture on Campy agar

Diagnosis:• Endoscopic examination with

biopsy.• Culture of the gastric mucosa.

Azithromycin Erythromycin or azithromycin Bismuth salts and/or a protein pump inhibitor plus two antibiotics

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