Campylobacter

The family Campylobacteriaceae includes aerobic or microaerophilic, motile, vibrioid, non-spore-forming, Gram-negative bacteria of three genera: Campylobacter, Helicobacter, and Arcobacter. The composition of the genera is constantly being refined as new data are obtained.

Campylobacteriosis is an infectious disease characterized by an acute onset, fever, and gastrointestinal tract lesions. Studies conducted in recent years have shown that in a number of countries, campylobacter causes from 3 to 15% of all cases of acute intestinal diseases.

In infectious pathology of humans and animals, the most important role is played by the species C. jejuni, C. coli and C. lari, causing acute intestinal infections of similar clinical course. Based on the ability to grow at a relatively high incubation temperature (42 °C), they are combined into one group of thermophilic campylobacter. Among other mesophilic species of campylobacter, preferring a moderate incubation temperature (37 °C), a known role in human pathology is played by C. fetus, which is often the causative agent of arthritis, meningitis, vasculitis; the species C. concisus and C. sputorum are regarded as commensals of the oral cavity, possibly playing a role in the pathogenesis of periodontitis, and the species C. fennelliae, C. cinaedi and C. hyointestinalis are found in the large intestine in immunodeficiencies of various genesis.

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Morphology of Campylobacter

Campylobacter are gram-negative, thin, spirally curved rods measuring 0.2-0.3 x 0.5-5.0, sometimes up to 8.0 µm. They can form one full (or slightly more) turn of the spiral, can be C- or S-shaped, or resemble seagull wings when two cells are connected in a short chain. In old cultures, the cells can have a coccoid or hyperspiral shape. They do not form spores and capsules, have 1 or 2 (sometimes up to 5) polar flagella, providing them with high motility with a rapid corkscrew-like or helical translational movement. Flagella can be 2-3 times longer than the cell. Motility is better seen with dark-field or phase-contrast microscopy. The G + C content in DNA is 30-38 mol %.

Biochemical properties of campylobacter

Campylobacter are chemoorganotrophs. Being thermophiles, they are capable of growth at a temperature of 37-44 °C, but not at 25 °C. Most campylobacter are microaerophiles and capnophiles, the optimal atmosphere for cultivating pathogenic species has the composition: O2 - 5%, CO2 - 10%, N2 - 85%. Some campylobacter can behave as obligate anaerobes when grown. They release energy from amino acids and tricarboxylic acids, but not from carbohydrates, which they are not capable of oxidizing and fermenting.

For the cultivation of campylobacter, special nutrient media are often used, which are based on the media for the isolation of brucellae. However, it is necessary to add substances to these media that increase the aerotolerance of campylobacter and reduce the redox potential of the medium (blood, sodium thioglycolate, sodium metabisulfite, sodium pyruvate, Fe2+ sulfate). Meat, liver, and blood media are usually used, and antibiotics (novobiocin, cyclohexamide, bacitracin, trimethoprim) are often added to them to suppress the accompanying microflora. On nutrient media, campylobacter growth is usually observed after 2-4 days. On liquid nutrient media, diffuse turbidity with a pronounced sediment that is difficult to break up is observed. On semi-liquid media, they grow in the form of a diffuse turbid ring 1-4 mm thick under the surface of the medium. If campylobacter grows under conditions of strict anaerobiosis, turbidity of the entire medium is observed.

On solid media with blood, campylobacters form two types of colonies:

• round, irregular in shape, with smooth edges, 2-8 mm in diameter, colorless or light gray, transparent, homogeneous (resembling drops of water); with prolonged cultivation, they can acquire a silvery-matte shade;
• Colonies of regular round shape, with smooth edges and a diameter of 1-2 mm, with a shiny convex surface, transparent, homogeneous; in old colonies the center is denser than the periphery, and a yellowish pigment may form. The consistency of the colonies is not viscous, there is no hemolysis zone.

Campylobacter are oxidase-positive, do not hydrolyze gelatin and urea, and are negative in reactions with methyl red and Voges-Proskauer. They produce cytochrome oxidase and do not grow on Russell medium; they are divided into two groups according to their ability to form catalase: catalase-positive (C. fetus, C. jejuni) and catalase-negative (C. sputorum and C. concisus). Some of their species can form hydrogen sulfide, grow in the presence of 1 and 3.5% NaCl, brilliant green, nalidixic acid, cephalothin, hydrolyze sodium hippurate, and form a yellow pigment. Interspecies differentiation is based on these properties.

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Antigenic structure of campylobacter

Campylobacters have O-, H- and K-antigens. C. jejuni and C. coli, which most often cause diseases in humans, are serologically heterogeneous. Foreign literature describes 55 serogroups that differ in the thermostable O-antigen. It has been established that strains isolated from humans give an agglutination reaction only with serum from humans, and they are not agglutinated by serum from immunized animals. It can be assumed that strains specific to humans are being formed.

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Campylobacter pathogenicity factors

Campylobacter has a whole complex of virulence factors, including lipopolysaccharide, enterotoxin (causes diarrhea), cytotoxin that damages the mucous membrane of the colon in humans, etc.

At room temperature and, especially, at low temperatures, the resistance of campylobacter to the action of environmental factors is very high: they can remain viable for 1-5 weeks in food products, tap and waste water, milk, urine, and excrement. Campylobacter are very sensitive to heating above 50 °C, exposure to direct sunlight and ultraviolet light and air, drying, low and high pH values of the environment, and are sensitive to the action of disinfectants in working concentrations.

Immunity

Campylobacters are highly immunogenic. Antibodies appear in the blood early in the disease and in fairly high titers. The titer D° 1:5000 occurs already on the 5th day of the disease; having reached the maximum, the antibody titers (IgG) slowly decrease over a long period of time and after a month may still be quite high.

Epidemiology of campylobacteriosis

Campylobacter (especially thermophilic) are found in all species of wild and domestic animals and birds, many of which are their natural reservoirs (cattle and small cattle, chickens, starlings, sparrows, parrots, etc.). Farm animals should be considered the main reservoir of campylobacter, additional ones are sick people and domestic animals, wild urban birds and rodents. The main route of transmission of the infection is food (raw milk, slaughtered poultry, beef, pork), additional ones are water (river and sea water contaminated with animal excrement) and household (gross violations of sanitary and hygienic standards when caring for sick people and animals, as well as when cooking meat products). Campylobacteriosis is characterized by pronounced summer seasonality with an almost complete absence of morbidity in the winter months. Most often, the disease is recorded as sporadic cases ("traveler's diarrhea"), occasionally - in the form of more or less large outbreaks. After an illness, in people who are not treated with antibiotics, bacteria are excreted in the feces for quite a long time, for 2-5 weeks, and sometimes up to 10 weeks.

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Symptoms of Campylobacteriosis

In humans, campylobacteriosis occurs mainly in the form of enteritis and enterocolitis, although diseases of other localizations have been described: septicemia, endocarditis, pericarditis, meningitis; lesions of extraintestinal localization are more often observed in older people or in patients with reduced resistance of the body.

The incubation period is 1-10 days, more often 1-5 days. The onset of the disease is often acute, less often subacute. Moderate intoxication and diarrhea (up to 10-20 times a day), pain in the lower abdomen are usually observed. In half of the cases, there is blood in the stool, less often - dehydration. The disease occurs more often and is more severe in children aged 1 to 3 years. Pathogenesis and severity are directly dependent on the factors present in a given strain of campylobacter, as well as on the number of bacteria that have entered the body.

Laboratory diagnostics of campylobacteriosis

Microscopic, bacteriological and serological methods are used to diagnose campylobacteriosis. The microscopic method is used as an indicative one. A thin smear of feces fixed on a flame is stained with a 1% aqueous solution of basic fuchsin for 10-20 s, then washed with water. Since most other bacteria require 2-5 minutes to stain, only campylobacter usually manages to stain in a smear in 10-20 s. In native material, they have a characteristic shape (S-shaped short chains in the form of seagull wings, less often - C-shaped with drawn-out ends).

The main diagnostic method is bacteriological. The material for sowing is feces or rectal contents, sometimes blood, as well as water, milk, other food products, washings from objects, etc. Sowing is done on special nutrient media, microaerophilic conditions are created and incubated at a temperature of 37 and 42 °C. After obtaining typical colonies, the culture is identified by a set of characteristics.

The serological method of research plays a very important role in large-scale epidemiological studies, but its role in the diagnostics of campylobacteriosis is small. The agglutination reaction is carried out with autostrains, it is possible with a living museum culture, but with a formalinized culture the results are clearer. The most sensitive methods are RIF and IFM. RSC, latex agglutination, immunoelectrophoresis, RPGA can also be used.

Treatment of campylobacteriosis

Antibiotics are used to treat campylobacteriosis; gentamicin and erythromycin are the most effective, kanamycin, chloramphenicol and semi-synthetic penicillins are less effective.

How to prevent campylobacteriosis?

Specific prevention has not been developed; other preventive measures include strict adherence to standards for processing, transporting and storing food products, personal hygiene rules, and protecting water bodies from pollution by wastewater (especially livestock farms).