Vibrio cholerae Overview Quiz

Lecture 8: Vibrio, Campylobacter, Helicobacter

• Lecture date: 11/3/2022
• Focuses on microbiology of Vibrio, Campylobacter, and Helicobacter species.
• Key topics include biological characteristics, pathogenesis, diagnostic tests, treatment, epidemiology, prevention, and control of diseases associated with each group.

Vibrios

• Main biological characteristics of Vibrio cholerae
• Pathogenesis of Vibrio cholerae diseases, focusing on enterotoxin function.
• Diagnostic laboratory tests for Vibrio cholerae diseases.
• Treatment, epidemiology, prevention, and control of Vibrio cholerae diseases.
• Overview of Vibrio parahaemolyticus and other Vibrio species, Aeromonas, and Plesiomonas.

Campylobacters

• Main biological characteristics of Campylobacter species.
• Diseases caused by Campylobacter, covering pathogenesis and pathology.
• Diagnostic laboratory tests.
• Epidemiology and prevention of diseases caused by Campylobacter.

Helicobacters

• Main biological characteristics of Helicobacter species.
• Pathogenesis and associated diseases.
• Diagnostic laboratory tests.

Taxonomy of Vibrios

• Vibrionaciae family
• Non-enteric, fermentative, Gram-negative rods.
• Oxidase-positive and motile by means of polar flagella.
• Includes Vibrio cholerae, V. vulnificus, V. parahaemolyticus, Aeromonas, and Plesiomonas.

Vibrio sp. general characteristics

• Gram-negative rods with polar sheathed flagella in broth and peritrichous unsheathed flagella in solid media.
• Appear curved in clinical specimens but are small, straight rods after culture.
• Facultatively anaerobic.

Vibrio cholerae

• Prefers alkaline pH (8.0-9.5) over acidic conditions.
• Distinguished from other Vibrio species by biochemical reactions, LPS O antigenic structure, and production of cholera toxin (CT).
• Over 200 serotypes, but only O1 and O139 cause cholera.
• O1 variant, a biotype, includes biogroup El Tor.
• O139 strains resemble O1 El Tor, but also produce a polysaccharide capsule.
• All cholera-causing strains produce a colonizing factor called toxin-coregulated pilus (TCP), which is regulated with cholera toxin (CT).
• In aquatic environments V. cholerae produce polysaccharide biofilms for cell-cell adhesion and attachment to surfaces.

Cholera Toxin (CT)

• An A-B type ADP-ribosylating toxin.
• Its molecule consists of two toxic subunits (A₁ and A₂) regulated with five binding (B) units.

Mechanism of action of cholera toxin

• Toxin binds ganglioside receptors on cells.
• A1 subunit translocates into cells.
• A1 subunit activates adenylate cyclase.
• This increases cAMP levels in the cell, leading to excessive chloride, potassium, bicarbinates secretion and associated with water molecules output from the cell.

Vibrio cholerae (cont'd)

• Clinical infection involves acute diarrheal diseases, spread through contaminated water, seafood, etc., and incubaion period of 2 days.
• Stools are "rice water" type.
• Dehydration is a common cause of death.
• About 60% of Vibrio cholerae O1 infections are asymptomatic, and 75% of El Tor infections are asymptomatic.
• Incubation period is 1-4 days in symptomatic cases, varying with innoculum size.
• Symptoms are nausea, vomiting, and profuse diarrhea with abdominal cramps.
• Mortality rate is 25-50% without treatment.
• V. cholerae O1 is frequently associated with Asiatic cholera or epidemic cholera; widespread in India and Bangladesh, and on Gulf coast of US.
• V. cholerae O139 is very similar to O1 El Tor biotype but does not produce O1 LPS, has all the necessary genes to make the antigen, and produces a polysaccharide capsule.

Voges-Proskauer test

• Detects acetoin, an intermediate of a bacterial fermentation pathway.
• Used to differentiate various bacterial species.

Vibrio sp. (cont'd)

• Key indicators of Vibrio infection include recent intake of raw seafood, especially oysters, recent travel to endemic areas, typical stool features, and accidental exposure to marine environments.

Culture

• Vibrio species can be cultured on Thiosulfate-Citrate-Bile-Salt agar (TCBS).

Difference between Vibrios and Aeromonas

• Vibrio species are susceptible to the compound O/129, whereas Aeromonas species are resistant.
• Most Vibrio species are halotolerant and/or halophilic, requiring NaCl for growth, whereas Aeromonas do not require NaCl for growth

Vibrio parahaemolyticus

• Second most common Vibrio species causing gastroenteritis (commonly in Japan, known as "Summer diarrhea").
• Usually caused by intake of raw/improperly cooked seafood, oysters particularly.
• Self-limiting symptoms in most cases, typically mild symptoms: watery diarrhea, moderate cramps, or vomiting.

Vibrio vulnificus

• Found in marine environments.
• Two major categories of infections:
  • Primary septicemia (following contaminated shellfish consumption, especially raw oysters) with increased risk for patients with liver dysfunction, high iron levels
  • Wound infections (following traumatic aquatic wound exposure).
• High mortality rate (about 50%) in septicemic infections, cases often proceed fast, leading to bullous skin lesions, cellulitis, and myositis with necrosis.

Helicobacteria

• Helicobacter pylori (H. pylori):
  • Discovered in stomachs of patients with gastritis and stomach ulcers by Marshall and Warren.
  • H. pylori is now widely recognized as a major cause of peptic ulcers.
  • Very common in developed countries, but most infected individuals do not have ulcers.
  • It is a spiral gram-negative bacteria, oxidase-positive and catalase-positive, with multiple polar flagella.
  • Believed to be transmitted orally through tainted food or water, and also through belching or gastro-esophageal reflux.
  • Significant components for pathogenicity are cytotoxin-associated (CAG) and vacuolating cytotoxin (Vac) genes.
  • It is highly motile, even in thick mucus, and it is believed that its motility allows it to reach the epithelial surfaces of the stomach/duodenum.
  • Strongly associated with gastric and duodenal ulcers and low-grade inflammatory processes.
  • H. pylori does not invade the gastric epithelium; instead, it causes inflammation.
  • Strongly urease-positive and easy to detect using the 14C-labeled urea breath test. It is used to detect H. pylori infection in the breath by measuring the amount of 14CO₂ exhaled following ingestion of a urea tablet labeled with 14C.
  • Triple therapy (Metronidazole, Bismuth subsalicylate or Bismuth subcitrate and Amoxicillin or Tetracyclines) eradicates H. pylori in 70 to 95% of patients.
  • High prevalence in developing countries.

Campylobacters

• Campylobacter jejuni:
  • Most common cause of bacterial gastroenteritis worldwide often due to direct or indirect exposure to infected animals or contaminated water/dairy products.
  • Usually caused by contaminated water/dairy products or improperly cooked poultry .
  • Often cause severe diarrhea; sometimes can be life-threatening, and can be a trigger for Guillain-Barre syndrome (GBS).
  • Can be cultured in selective media.

Lab diagnosis and selective media

• Feces are refrigerated and examined within hours.
• Rectal swabs, blood samples are also used in diagnosis.
• Care must be taken to avoid oxygen exposure
• Selective isolation methods (e.g. filtration).
• Enrichment broths and selective media are used.
• Microscopy may help to confirm the diagnosis.
• Susceptibility to antibiotics (e.g. nalidixic acid, cephalothin) can be used to determine the course of treatment.
• Charcoal-based selective medium agar (CSM) is used to isolate Campylobacter jejuni.

Treatment, Prevention & Control

• For Vibrio gastroenteritis: water and electrolyte replacement and, in severe cases, antibiotics
• For Campylobacter infections: self-limiting gastroenteritis is often just supportive care, but in severe cases, antibiotics can shorten excretion period.
• For H. pylori: triple therapy, which uses a combination of antibiotics and bismuth compound, with an added acid-suppressing agent if needed.

Complication

• Rare but complications include reactive arthritis, hemolytic uremic syndrome, and bloodstream infections.

History

• Cholera: Identified by Hippocrates, 500 BC, and by the Italian physician Filippo Pacini in 1854.
• Campylobacter: Recognized as a cause of gastroenteritis in the mid-1970s.
• H. pylori: Identification of H. pylori as the primary cause of stomach ulcers was a landmark moment in medical research and was initially met with skepticism.

Epidemics/Outbreaks

• Global trends in outbreaks/epidemics of Vibrio and Campylobacter infections.
• Geographical distribution of these infections.

Test your knowledge on Vibrio cholerae, the bacterium responsible for cholera. This quiz covers key aspects such as biochemical reactions, pathogenic factors, diagnosis methods, and treatment protocols. Challenge yourself to learn about this important microorganism and its impact on public health.