Campylobacter

General characteristics and morphology

The genus name comes from the Greek word campylos, which translates as "crooked" or "curved". To date, about 18 species of Campylobacter have been described, among which C. jejuni (the main pathogen), C. fetus, and C. coli are of the greatest clinical significance.

Morphologically, they are small Gram-negative (G-) microorganisms: their length ranges from 0.5–5 µm, and their thickness from 0.2–0.5 µm. The cells have a characteristic convoluted shape, resembling a comma or the Latin letter S. In smears, they are often arranged in pairs, making their clusters look like "seagull wings in flight".

Campylobacters are motile due to the presence of a single polar flagellum (monotrichous). They do not form spores or capsules. A distinctive feature is pronounced polymorphism: as the bacterial culture ages, the curved forms transform into coccoid forms.

Cultural and biochemical properties

Microorganisms are classified as microaerophiles and capnophiles. Their successful growth requires a specific gas environment with a reduced oxygen concentration and an increased carbon dioxide content. The optimal pH level is 7.0, although temperature preferences depend on the specific species (most often 37 °C or 42 °C, less commonly 25 °C).

Campylobacters are fastidious regarding nutrient media. They are cultivated on complex substrates enriched with blood, hemin, amino acids, and protein hydrolysates. To suppress the growth of accompanying microflora (ensure medium selectivity), antibiotics are necessarily added to the composition.

• Metabolism: strictly respiratory type. Bacteria are unable to ferment sugars.
• Energy sources: organic acids, including amino acids.
• Enzymatic activity: weak. Microorganisms are oxidase- and catalase-positive, reduce nitrates, and produce hydrogen sulfide ($H_2S$).

Pathogenicity factors and antigenic structure

Bacteria possess somatic (O) and flagellar (H) antigens. Based on their combinations, about 60 serovars are distinguished. The cells contain plasmids that determine the resistance of microorganisms to antibacterial drugs.

The pathogenic potential is due to the following factors:

1. Endotoxin — a structural component of the cell wall (lipopolysaccharide) released upon bacterial death.
2. Exotoxins (produced by certain strains): a cholera-like enterotoxin that provokes profuse diarrhea, and a cytotoxin that directly damages host cells.

Campylobacters have low resistance in the external environment. They are rapidly inactivated by heating, exposure to conventional disinfectants, and other physical and chemical factors.

Epidemiology and clinical manifestations

Campylobacteriosis is a zooanthroponosis with a ubiquitous distribution. Natural human susceptibility to the infection is extremely high. The incidence is recorded year-round, although a summer-autumn epidemic peak is typical.

• Reservoir and source: mainly farm animals and poultry. A sick person rarely acts as a source of infection.
• Routes of transmission: alimentary (foodborne), waterborne, contact-the-transmission (household), and sexual.

Pathologies associated with Campylobacter are divided into four groups:

1. Gastrointestinal tract lesions (enterocolitis, diarrhea) with potential generalization up to sepsis.
2. Local extraintestinal forms (endocarditis, central nervous system lesions — encephalitis and meningitis).
3. Purulent-inflammatory diseases in newborns.
4. Oral cavity pathologies.

Classical gastroenteritis develops after an incubation period (2–3 days). The disease manifests acutely: symptoms of intoxication, fever, vomiting, and diarrhea appear. The clinical picture usually subsides within 10 days.

Diagnostics, treatment, and prevention

The main diagnostic method is bacteriological. Feces, vomit, or gastric lavage fluids are collected for examination. Inoculation is performed on blood or erythritol agar supplemented with iron-sulfulfite-pyruvate components. Species differentiation relies on the ability of strains to grow at different temperatures.

During bacterioscopy of feces smears, microorganisms with a characteristic morphology ("flying seagull/swallow") can be detected. Serological methods (CF, HAI, agglutination test) and rapid diagnostics using direct DFA with fluorescent sera are also used.

For etiotropic treatment, antibiotics are prescribed; erythromycin and ciprofloxacin serve as the drugs of choice. Specific prevention (vaccination) has not been developed. Combating the infection is based on sanitary and anti-epidemic measures, which are similar to the prevention measures for salmonellosis.

Class and exam questions

What else to study on this topic

• Mechanism of action of Campylobacter cholera-like enterotoxin on enterocytes.
• Features and compositions of selective nutrient media for the isolation of microaerophiles.
• Pathogenesis of the development of extraintestinal forms of infection (meningitis, endocarditis).
• The role of plasmids in the formation of antibiotic resistance mechanisms in Campylobacter.

Other topics from the section 'Spirochetes and spiral bacteria (Treponemes/syphilis, Borrelia/Lyme disease and relapsing fevers, Leptospira, Campylobacters, Helicobacters)'

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