Classification
Gram-negative bacteria:
Most bacteria can be classified according to a lab procedure called Gram staining.
Bacteria with cell walls that have a thin layer of peptidoglycan do not retain the crystal violet stain utilized in Gram staining. These bacteria do, however, retain the safranin counterstain and thus appear as pinkish-red on the stain, making them gram negative. These bacteria can be further classified according to morphology (diplococci, curved rods, bacilli, and coccobacilli) and their ability to grow in the presence of oxygen (aerobic versus anaerobic). The bacteria can be more narrowly identified by growing them on specific media (triple sugar iron (TSI) agar) where their enzymes can be identified (urease, oxidase) and their ability to ferment lactose can be tested.
* Stains poorly on Gram stain
** Pleomorphic rod/coccobacillus
*** Require special transport media
General Characteristics
Basic features
General characteristics of Campylobacter species include:
- Gram-negative
- Ribbon or S-shaped bacilli
- Polar flagella
- Microaerophilic or partially anaerobic
- Thermophilic:
- Preferred growth at 37–42°C (98.6–107.6°F)
- Key factor used to distinguish from Vibrio cholerae, which is also a gram-negative, comma-shaped bacilli
- Fastidious growth requirements: CO2-enriched environment
- Oxidase positive
- Catalase positive: split hydrogen peroxide into water and oxygen
Clinically relevant species
- C. jejuni
- C. coli
- C. upsaliensis
- C. fetus
Campylobacter bacteria
Scanning electron micrograph depicts an S-shaped organism with a single, polar flagella.
Epidemiology
- Campylobacter is the leading cause of acute diarrhea worldwide.
- Most common in young children and young adults
- Slight male predominance
Pathogenesis
Reservoirs
- C. jejuni: intestinal tract of animals, primarily poultry
- C. coli: intestinal tract of pigs
- C. upsaliensis: intestinal tract of dogs and cats
- C. fetus: intestinal tract of cattle and sheep
Trasmission
- Food contamination (most common):
- Consumption of raw or undercooked meat
- Cross-contamination from raw meat
- Unpasteurized milk
- Water-borne (contaminated unchlorinated water)
- Fecal–oral transmission
- Direct contact with animals or carcasses: usually associated with occupational exposure (cattle, dogs, and cats)
Pathogenesis factors
- Bacterial load: higher numbers more likely to produce illness
- Virulence:
- Flagella: ability to move through mucus
- Superficial adhesins, chemotactic factors: mediate attachment to intestinal mucosa
- High-molecular-weight plasmids: increase invasiveness
- Host immunity:
- Primarily humoral (immunoglobulin A (IgA), IgM, IgG, complement)
- May generate autoimmune response through molecular mimicry
Campylobacter pathogenesis
When pathogens are embedded in the mucosal surfaces, they produce a variety of toxins which include endotoxin, enterotoxins, and cytotoxins. The body reacts by activating the complement cascade which results in the inactivation of organisms. The humoral immune system reacts by creating antibodies, which then target the Campylobacter and cause molecular mimicry to the human neurological and musculoskeletal systems. This results in an autoimmune response.
Clinical Presentation
Gastroenteritis
- Abdominal pain/cramping
- Fever
- Diarrhea
- Bloody diarrhea, especially in children.
- Incubation period: 3 days
- Duration: self-limited, lasts approximately 7 days
- Treatment: supportive
Complications (autoimmune)
- Guillain-Barré syndrome:
- Usually occurs 1–2 weeks after onset of diarrhea
- Symmetric ascending paralysis due to molecular mimicry of peripheral, Schwann cells
- Reactive arthritis:
- Classic triad: conjunctivitis, urethritis, arthritis
- Usually occurs 1–2 weeks after onset of diarrhea
- More commonly associated with HLA-B27 phenotype
Prevention
- Primarily through safe food-handling practices
- Cooking poultry to proper temperatures
- Avoiding cross-contamination
- Hand-washing practices for anyone with diarrheal illnesses or direct contact with farm animals
References
- Allos B.M. (2019). Microbiology, pathogenesis, and epidemiology of Campylobacter infection. UpToDate. Retrieved January 2, 2021, from https://www.uptodate.com/contents/microbiology-pathogenesis-and-epidemiology-of-campylobacter-infection?search=campylobacter&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2
- Allos B.M. (2019). Clinical manifestations, diagnosis, and treatment of Campylobacter infection. UpToDate. Retrieved January 2, 2021, from https://www.uptodate.com/contents/clinical-manifestations-diagnosis-and-treatment-of-campylobacter-infection?search=campylobacter&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
