L13. Vibrio & Other Gram-Negative Bacilli

What are Vibrionaceae?

A group of gram-negative bacilli that infect the gastrointestinal tract but are not considered enteric bacilli

What is the morphology of Vibrio species?

Gram-negative, comma-shaped bacilli, motile via a single thick polar flagellum (monotrichous).

What is the oxygen requirement of Vibrio species?

Facultative anaerobes.

What biochemical test differentiates Vibrio from gram-negative enteric bacilli?

Oxidase test (Vibrio is oxidase-positive, enteric bacilli are oxidase-negative).

Which gram-negative enteric bacillus also has a positive string test like Vibrio?

Klebsiella pneumoniae.

What are the two toxigenic serotypes of Vibrio cholerae?

O1 (with Classical and El Tor biotypes) and O139.

What are the three serotypes of Vibrio cholerae O1?

Inaba (A & C), Ogawa (A & B, small C), Hikojima (A, B, C).

What are the key biochemical differences between V. cholerae Classical and El Tor biotypes?

• El Tor: VP-positive, erythrocyte agglutination-positive, Polymyxin B-resistant.

• Classical: VP-negative, erythrocyte agglutination-negative, Polymyxin B-sensitive.

What is the primary virulence factor of Vibrio cholerae?

Choleragen (cholera enterotoxin), which increases cAMP, leading to fluid loss and diarrhea.

How does cholera toxin cause diarrhea?

Subunit B allows entry of subunit A, which increases adenylate cyclase activity → increased cAMP → loss of Na+, Cl-, H2O, and K+.

Why does Vibrio cholerae require a high infectious dose (10⁶-10¹¹ CFU)?

It is sensitive to stomach acid. More bacteria are needed to survive and reach the intestines.

How is Vibrio cholerae transmitted?

Contaminated food, water, and insects (houseflies).

What is the incubation period of cholera?

2–3 days.

What are the symptoms of cholera?

Profuse watery diarrhea (“rice water stools”), dehydration, muscle cramps, scaphoid abdomen, weak pulse.

What laboratory media are used for Vibrio cholerae?

• Tellurite Taurocholate Gelatin Agar (TTGA) – Transparent colonies with a cloudy halo.

• Thiosulfate Citrate Bile Salt Sucrose (TCBS) Agar – Flat yellow colonies.

What are the biochemical test results for Vibrio cholerae?

• TSI: Acid slant/acid butt, no gas, no H2S.

• Oxidase test: Positive.

• String test: Positive.

What is the primary reservoir for Vibrio parahaemolyticus?

• Marine environments and seafood.

How is Vibrio parahaemolyticus transmitted?

Consumption of raw or undercooked seafood.

What are the symptoms of Vibrio parahaemolyticus infection?

Explosive watery diarrhea, nausea, vomiting, abdominal cramps, low fever.

What is the key laboratory finding that differentiates Vibrio parahaemolyticus from Vibrio cholerae?

On TCBS agar, V. parahaemolyticus produces green colonies (sucrose-negative), while V. cholerae produces yellow colonies (sucrose-positive).

What is the clinical significance of Vibrio vulnificus?

Causes wound infections, septicemia, and bacteremia (often linked to raw oyster consumption).

What is the morphology of Campylobacter species?

Gram-negative, curved, comma-shaped, or S-shaped rods with a single polar flagellum

What is the oxygen requirement of Campylobacter?

Microaerophilic (requires 5% oxygen, not 20%).

Which Campylobacter species grows well at 42°C?

Campylobacter jejuni.

How is Campylobacter jejuni transmitted?

Fecal-oral route, contaminated food and water, contact with infected animals.

What disease is caused by Campylobacter jejuni?

Enterocolitis with foul-smelling watery diarrhea, followed by bloody stools, fever, and abdominal pain

How is Campylobacter jejuni diagnosed?

Stool culture on Skirrow’s medium (Vancomycin, Trimethoprim, Polymyxin) incubated at 42°C under microaerophilic conditions.

What test differentiates Campylobacter jejuni from Campylobacter intestinalis?

Nalidixic acid sensitivity (C. jejuni is sensitive, C. intestinalis is resistant).

Who discovered Helicobacter pylori?

Barry Marshall and Robin Warren.

What is the morphology of Helicobacter pylori?

Gram-negative, curved spiral-shaped bacilli with multiple flagella (lophotrichous).

What diseases are caused by Helicobacter pylori?

Gastritis, peptic ulcers, and gastric carcinoma.

How does H. pylori survive in the stomach?

Produces urease, which breaks down urea into ammonia, neutralizing gastric acid.

What is the laboratory diagnosis for H. pylori?

• Histology (H&E stain, Warthin-Starry silver stain, Giemsa stain).

• Culture on Columbia agar or CAMPY-CVA.

• Urease breath test (detects CO2 from urea breakdown).

What is the urease breath test used for?

Detects H. pylori by measuring CO2 in exhaled air after ingesting labeled urea.

What is the treatment for H. pylori infection?

Triple therapy: PPI (omeprazole) + clarithromycin + amoxicillin/metronidazole.