Other Gram-negative rods !
- Bacteria
Curved rods, coccobacilli and non-fermenters: H. pylori, Vibrio, Pseudomonas, Haemophilus, Bordetella, Legionella and the zoonoses.
Updated 2026-11-01
What they are
A working group of Gram-negative rods that are not Enterobacterales. It holds the curved gut rods (Vibrio, Campylobacter, Helicobacter), the hospital non-fermenters (Pseudomonas, Acinetobacter), the respiratory coccobacilli (Haemophilus, Bordetella, Legionella) and the zoonotic bacteria (Bartonella, Brucella, Francisella). Gram-variable Gardnerella sits here for its role in vaginosis.
What they share
- Most are oxidase-positive (Vibrio, Campylobacter, Helicobacter, Pseudomonas)
- Several need special media: chocolate agar with factors X and V (Haemophilus), BCYE (Legionella), Bordet-Gengou or Regan-Lowe (Bordetella), TCBS (Vibrio)
- The zoonoses strike people who work with animals or animal products
- Pseudomonas and Acinetobacter: multidrug-resistant in intensive care units
Microorganisms in this group
- Helicobacter pyloriA bacterium that lives in the stomach, usually from childhood. It causes gastritis and ulcers and raises the risk of stomach cancer.Exam priority: high
- Vibrio choleraeA bacterium in contaminated water that causes cholera: watery diarrhea so heavy it can kill by dehydration within hours.Exam priority: high
- Campylobacter jejuniA bacterium from undercooked chicken that causes diarrhea, often bloody; rarely it is followed by paralysis (Guillain-Barré).Exam priority: medium
- Pseudomonas aeruginosaA water and soil bacterium that attacks hospital, burn and cystic fibrosis patients, and resists many antibiotics.Exam priority: medium
- Acinetobacter baumanniiAn intensive care unit bacterium that survives on dry surfaces and resists nearly every antibiotic.Exam priority: medium
- Haemophilus influenzaeA throat bacterium. Type b caused meningitis and epiglottitis in children before the vaccine; capsule-free strains cause ear and sinus infections.Exam priority: medium
- Bordetella pertussisThe whooping cough bacterium: coughing fits that last weeks. In babies under one year it can cause apnea and death.Exam priority: medium
- Legionella pneumophilaA bacterium in water from cooling towers, showers and hot tubs. Inhaled, it causes severe pneumonia (Legionnaires' disease) or a mild fever.Exam priority: medium
- BartonellaBacteria carried by cats, sand flies and lice. B. henselae causes cat scratch disease; B. bacilliformis causes Andean Carrión disease.Exam priority: medium
- BrucellaLivestock bacteria that reach people through unpasteurized milk or cheese or contact with animals: a fever that comes and goes.For completeness
- Francisella tularensisA bacterium of rabbits, hares and rodents spread by ticks, deer flies, contact or air; it causes tularemia and is very infectious in the lab.For completeness
- Gardnerella vaginalisA bacterium that overgrows when vaginal lactobacilli are lost and causes bacterial vaginosis: gray discharge with a fishy smell.For completeness
Test yourself
Think of the answer, then tap the question to see it.
Which curved Gram-negative rods are oxidase-positive and cause diarrhea or gastritis?
Vibrio, Campylobacter and Helicobacter.
Which growth factors does Haemophilus influenzae need?
Factor X (hemin) and factor V (NAD), both supplied by chocolate agar.
On which medium does Legionella grow?
Buffered charcoal yeast extract (BCYE) agar with cysteine and iron.
Which Gram-negative non-fermenter is a classic cause of ventilator-associated pneumonia?
Pseudomonas aeruginosa (Acinetobacter baumannii as well).
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Pseudomonas aeruginosa (CDC, 2025); Chapter 8: Haemophilus influenzae (CDC, 2024); Cholera (WHO, 2026).
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Representative model, for educational purposes only.