Campylobacter jejuni
Also known as: campylobacter
Campylobacter jejuni is a curved, comma-shaped gram-negative bacterium and one of the most common causes of bacterial gastroenteritis worldwide. It is transmitted mainly through undercooked poultry and unpasteurized milk.
Campylobacter jejuni is a gram-negative, oxidase-positive, microaerophilic rod with a curved or S-shaped morphology and darting motility from polar flagella. It is distinctive for growing best at 42 °C, the body temperature of birds, which reflects its natural reservoir in poultry and other animal intestinal tracts. Laboratories isolate it on selective media incubated at that temperature under reduced oxygen.
Infection follows ingestion of contaminated food or water — undercooked chicken is the classic source, along with unpasteurized milk and contact with infected pets. After an incubation period of a few days, it produces a prodrome of fever and abdominal pain followed by inflammatory, often bloody diarrhea. The abdominal pain can be severe enough to mimic appendicitis, a presentation called pseudoappendicitis. Most cases are self-limited; when treatment is warranted, macrolides such as azithromycin are typically used.
Its exam significance rests largely on sequelae. C. jejuni is the most commonly identified antecedent infection in Guillain-Barré syndrome, an ascending paralysis caused by molecular mimicry between bacterial lipooligosaccharide and peripheral nerve gangliosides. It is also a recognized trigger of reactive arthritis. Those associations are what turn a routine diarrheal pathogen into a high-yield organism.
USMLE Step 1 microbiology covers C. jejuni among the other important bacteria, and questions almost always hinge on one of three details: the comma-shaped gram-negative morphology with growth at 42 °C, the poultry exposure history with bloody diarrhea, or the link to Guillain-Barré syndrome. Contrast it with the other invasive enteric pathogens — Salmonella, Shigella, and enterohemorrhagic E. coli — which share the bloody-diarrhea presentation.
Key takeaways
- Campylobacter jejuni is a curved gram-negative, oxidase-positive, microaerophilic rod that grows optimally at 42 °C.
- It is a leading cause of bacterial gastroenteritis, spread mainly by undercooked poultry and unpasteurized milk.
- Infection causes fever, cramping abdominal pain, and bloody diarrhea, sometimes mimicking appendicitis.
- It is the most common identified antecedent infection in Guillain-Barré syndrome and can trigger reactive arthritis.
- USMLE Step 1 tests its morphology, growth temperature, exposure history, and post-infectious complications.