Vibrionaceae Prof. Alaa H. Al-Charrakh

Babylon University, Iraq

Gastrointestinal pathogens of the family Vibrionaceae: Include the genera:

VibrioV. cholerae: cholera

V. parahaemolyticus: gastroenteritis

AeromonasA. hydrophila: gastroenteritis; wound infection

CampylobacterC. jejuni: gastroenteritis

HelicobacterH. pylori: gastritis; peptic ulcer; gastric cancer, MALToma

Vibrio cholerae-Gram-ve curved rod. Motile by a polar flagellum.

-Grow at a high pH (8.5- 9.0) and are rapidly killed by gastric acid.

-Oxidase-positive.

-Vibrio species inhabit marine environments, and are halophilic.

V. cholerae O1:

Sero-subtypes: Inaba, Ogava & Hikojima

Two biotypes of V. cholerae O1: classical and El Tor.

Hemolysin V-P test Polymixin B

classical - - sensitive

El Tor + + resistant

Antigenic structure & biological classification

O antigen: confers serological specificity.

Serogroups O1 and O139 cause cholera.

El Tor V. cholerae

• It was first identified in 1905 at a quarantine camp on

the Sinai Peninsula in El-Tor, Egypt. The vibrios were

found in the guts of six pilgrims returning from Mecca.

Cholera epidemics

- Are associated with V. cholerae O1

- None O1 V. cholerae (O139) reported

in Bangladesh in 1992

- In 2007, a lack of clean drinking water

in Iraq led to an outbreak of cholera. A

total of 181 people were infected, with 10

deaths reported. Basic water

sterilization became impossible in some

places due to restrictions on the

availability of chlorine for water

sterilization.

V. cholerae is pathogenic only for humans.

Mean infective dose: 108-1010. Gastric acid provides some protection.

Mouth intestine attach to the microvilli of the epithelial cells and multiply release cholera toxin.

Major virulence factors:

Toxin-coregulated pili (TCP): adherence to mucosal cells.

Enterotoxin (cholera toxin): produced by O1 and O139 strains.

Hemagglutinin-protease: releases bacteria from mucosal cells.

other enterotoxins, flagellum, siderophores.

Pathogenesis and Immunity

Clinical Diseases

Incubation period: 1-4 days.

-Sudden onset of nausea and vomiting, and profuse diarrhea with abdominal cramps; "rice water" stool (containing mucus, epithelial cells, and large numbers of vibrios)

-rapid loss of fluid and electrolytes profound dehydration that leads to circulatory collapse (hypovolemic shock).

Carrier state seldom exceeds 3-4 weeks.

The El Tor biotype causes milder disease than the classical biotype.

V. cholerae

Cholera Toxin

CT is a proteinaceous enterotoxin.

It composed of a AB subunit. The B subunit forms a pentameric structure that binds the CT to the receptor on the eukaryotic cells.

The A subunit contains the enzyma-tically active portion or the toxin

Proteolytic cleavage of the A subunit results in A1 and A2 peptide units which remain linked by a disulfide bond.

Once the A subunit is internalized by the eukaryotic cell, the disulfide bond

is reduced.

The A1 subunit contains a ADP-ribosyltransferase which covalently modifies

the G protein, which regulates adenylate cyclase. Adenylate cyclase

mediates the formation of cAMP

The increase in cAMP levels bring about the secretion of chloride and

bicarbonate from the mucosal cells into the intestinal lumen

Activation of adenyl cyclaseActivation of

adenyl cyclase

Pathogenesis of Cholera Toxin

INTESTINALCELL

ReceptorReceptor

+ NAD G-2-ADP-ribose + NicotinamideProtein G + NAD G-2-ADP-ribose + Nicotinamide+ NAD G-2-ADP-ribose + NicotinamideProtein G

ADP-ribosyulation of Protein G• Subunits B facilitate entry of subunit A (Active subunit) into cell• Subunit A cleaves nicotinamide from NAD and transfers the

remaining ADP-ribose to protein G (locked protein G)• Activates adenyl cyclase to convert ATP to cAMP - secretions

AA

AA

ATP cAMP secretions ATP cAMP secretions

Locked G proteinLocked G protein

AB

BB

BB B

Cholera toxin AB

BB

BB B

Cholera toxin

Specimens: mucus flecks from stool.

Smears: Dark-field or phase contrast microscopy may show the rapidly motile vibrios.

Culture: peptone agar, blood agar (pH near 9.0), or TCBS (thiosulfate-citrate-bile salts-sucrose) agar. Alkaline peptone broth can be used for enrichment.

Biochemical tests

Serological tests: slide agglutination tests using anti-O1 or O139 antiserum.

Diagnostic lab tests

Growth of V. cholerae on TCBS

Controls:

1. Improvement of sanitation and personal hygiene.

2. Isolation of patients, and their excreta be disinfected.

3. Vaccination: in development.

Treatment

Water and electrolyte replacement - most important.

Antibiotic treatment: tetracycline or trimethoprim-sulfamethoxazole.

- Halophilic

- Causes acute gastroenteritis following ingestion of contaminated seafood (e.g., raw fish or shellfish).

Incubation period: 5-72 hours.

Symptoms: sudden onset of nausea, vomiting, abdominal cramps, no or low grade fever, and watery (mostly) to bloody diarrhea.

V. parahaemolyticus

Campylobacter

Campylobacters contain pathogens for various animals, which

serve as reservoirs (Zoonotic). C. jejuni is a common cause of

diarrhea in humans.

Morphology

Small gram-negative rods with coma,

S or “gull wing" shapes.

Motile with a single polar flagellum.

C. jejuni, enteritis, and occasionally systemic invasion.

Campylobacter

Physiology and Structure

Microaerophilic: grows best in the presence of 5% O2 + 10%

CO2 (anaerobic jar plus gas generating pack).

Most Campylobacter pathogens can grow at 42 oC.

Oxidase- and catalase-positive.

Pathogenesis and Clinical diseases

C. jejuni

Infections are acquired from ingestion of contaminated food,

particularly, poultry.

Mouth multiply in the small intestine invade the

epithelium cause inflammation presence of RBC and

WBC in the stools.

Ingestion of about 104 bacteria is usually necessary to produce

infection.

Pathogenesis and Clinical Diseases

C. jejuni

Acute onset of crampy abdominal pain, profuse diarrhea that may be grossly bloody, headache, malaise, and fever. Usually self-limited (5-8 days).

Occasionally, the bloodstream is invaded and a clinical picture of enteric fever develop.

Guillain-Barré syndrome is an autoimmune disease of the peripheral nervous system resulting from infection by C. jejuni due to antigenic cross-reactivity between LPS and glycosphingolipids of the neural tissue in the peripheral nervous system.

Laboratory Diagnosis

Specimens: diarrheal stool

Smears: small, gram-negative "gull-wing" shaped rods.

Commercial kits for detection of specific antigens in the specimen.

Culture: selective media (e.g., Skirrow's medium and Camp BAP medium, in which blood, charcoal, and antibiotics are added), microaerophilic environment; 42 oC for C. jejuni.

Treatment, Prevention, and Control

Replacement of lost fluid and electrolytes.

Antibiotics used for severe infections or septicemia.

Prevention: proper preparation of food; avoidance of unpasteurized dairy products; preventing contamination of water supplies.

Helicobacter pylori

Spiral-shaped, gram-negative rod.

Highly motile with polar flagella.

Grow on complex media in microaerophilic (5% O2 and 10% CO2 ) conditions.

Morphology and Physiology

Physiology of H. pyloriGrows optimally at a pH of 6.0-7.0.

Able to survive in the stomach because

1. it stays deep in the mucus layer near the epithelial surface where physiological pH is present;

2. it produces a potent urease, which catalyzes production of ammonia that further neutralizes the acid;

3. It produces an acid-inhibitory protein that blocks acid secretion from parietal cells.

Pathogenesis and Clinical Diseases

Present on the gastric mucosa of less than 20% of persons

under 30

increases in prevalence to 40%-60% of persons age 60.

The prevalence reaches over 80% in developing countries.

H. pylori is associated with gastritis, peptic ulcer, gastric adenocarcinoma, gastric mucosa-associated lymphoid type (MALT) B-cell lymphomas.

Chronic gastritis is a risk factor for gastric carcinoma.

Steps of ulcer formation:

Colonization of the epithelial cells (inhibit gastric acid

secretion, neutralization of gastric acid, pass through the

gastric mucus, adhere to the epithelial cells)

Localized tissue damage by urease byproducts, enzymes

(mucinase, phospholipase etc.), and cytotoxins (vacuolating

cytotoxin A)

stimulation of inflammatory response by LPS.

Gastric ulcer formation with H. pylori

Mucous layer

Gastricepithelium

Basementmembrane

Helicobacterpylori

Mucus-secretingcell

LUMEN OF STOMACH

Mucous layer

Gastricepithelium

Basementmembrane

Helicobacterpylori

Mucus-secretingcell

LUMEN OF STOMACH

Bacteriainvade & multiply

Bacteriainvade & multiply

Epitheliumdestroyed bygastric acid

Ulcer formation

Epitheliumdestroyed bygastric acid

Ulcer formation

Laboratory diagnosis

Histological examination of gastric biopsies

Culturing biopsy specimens

Urease test is a rapid methods for detection of H. pylori in

biopsy specimens or pure culture.

Urea-breath test

Treatment, Prevention, and Control

Treatment:

Bithmus plus antibiotics

Omeprazole (a proton pump inhibitor), clarithromycin plus ammoxicillin or metronidazole

Humans are the main reservoir.

Mechanism of transmission is most likely oral-fecal, and improved hygienic standards can be helpful for prevention.