Klebsiella

The genus Klebsiella belongs to the family Enterobacteriaceae. Unlike the vast majority of genera in this family, bacteria of the genus Klebsiella have the ability to form a capsule. The genus Klebsiella includes several species.

The main role in human pathology is played by the species Klebsiella pneumoniae, which is divided into three subspecies: Klebsiella pneumoniae subsp. pneumoniae, Klebsiella pneumoniae subsp. and Klebsiella pneumoniae subsp. rhinoscleromatis. However, in recent years, new species of Klebsiella have been identified (Klebsiella oxytoca, Klebsiella mobilis, Klebsiella planticola, Klebsiella terrigena), which have not yet been studied well and their role in human pathology is being clarified. The genus name is given in honor of the German bacteriologist E. Klebs. Klebsiella are constantly found on the skin and mucous membranes of humans and animals. K. pneumoniae is a common causative agent of nosocomial infections, including mixed ones.

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Morphology of Klebsiella

Klebsiella are gram-negative ellipsoid bacteria, shaped as thick short rods with rounded ends, 0.3-0.6 x 1.5-6.0 µm in size, the capsular form is 3-5 x 5-8 µm in size. Sizes are subject to strong fluctuations, especially in Klebsiella pneumoniae. Flagella are absent, the bacteria do not form spores, and some strains have cilia. A thick polysaccharide capsule is usually visible; acapsular forms can be obtained by exposure of bacteria to low temperatures, serum, bile, phages, antibiotics, and mutations. They are located in pairs or singly.

Biochemical properties of Klebsiella

Klebsiella grow well on simple nutrient media, are facultative anaerobes, chemoorganotrophs. The optimum growth temperature is 35-37 °C, pH 7.2-7.4, but can grow at 12-41 °C. They are capable of growing on Simmons medium, i.e. using sodium citrate as the only carbon source (except for K. rhinoscleromatis). On dense nutrient media they form turbid mucous colonies, and in young 2-4-hour colonies, ozena bacteria are located in scattered concentric rows, rhinoscleromas are concentric, pneumoniae are loop-shaped, which is easily determined by microscopy of the colony with low magnification and can be used to differentiate them. When growing in MPB, Klebsiella cause uniform turbidity, sometimes with a mucous film on the surface; on semi-liquid media, growth is more abundant in the upper part of the medium. The content of G + C in DNA is 52-56 mol%.

Klebsiella ferment carbohydrates to form acid or acid and gas, reduce nitrates to nitrites. They do not liquefy gelatin, do not form indole and hydrogen sulfide. They have urease activity, do not always curdle milk. The least biochemical activity is expressed in the causative agent of rhinoscleroma.

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Antigenic structure of Klebsiella

Klebsiella has O- and K-antigens. Klebsiella is divided into 11 serotypes by the O-antigen, and into 82 by the capsular K-antigen. Serological typing of Klebsiella is based on the determination of K-antigens. Group-specific antigen is found in almost all strains of Klebsiella. Some K-antigens are related to K-antigens of streptococci, Escherichia coli and Salmonella. O-antigens related to O-antigens of E. coli have been found.

The main pathogenic factors of Klebsiella are K-antigen, which suppresses phagocytosis, and endotoxin. In addition, K. pneumoniae can produce heat-labile enterotoxin, a protein similar in its mechanism of action to the toxin of enterotoxigenic E. coli. Klebsiella have pronounced adhesive properties.

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Epidemiology of klebsiellosis

Klebsiella is most often a hospital-acquired infection. The source is a sick person and a carrier of bacteria. Both exogenous and endogenous infections are possible. The most common routes of transmission are food, airborne, and contact-household. The most common transmission factors are food products (especially meat and dairy), water, and air. In recent years, the incidence of Klebsiella has increased, one of the reasons for this is the increased pathogenicity of the pathogen due to a decrease in the resistance of the human body. This is also facilitated by the widespread use of antibiotics that change the normal ratio of microorganisms in the natural biocenosis, immunosuppressants, etc. It should be noted that Klebsiella has a high degree of resistance to various antibiotics.

Klebsiella are sensitive to the action of various disinfectants, and die within 1 hour at a temperature of 65 °C. They are quite stable in the external environment: the mucous capsule protects the pathogen from drying out, so Klebsiella can survive in soil, dust in wards, on equipment, and furniture at room temperature for weeks and even months.

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Symptoms of Klebsiella

Klebsiella pneumoniae most often causes a disease that occurs as an intestinal infection and is characterized by an acute onset, nausea, vomiting, abdominal pain, diarrhea, fever and general weakness. The duration of the disease is 1-5 days. Klebsiella can cause damage to the respiratory organs, joints, meninges, conjunctiva, genitourinary organs, as well as sepsis and purulent postoperative complications. The most severe is the generalized septicopyemic course of the disease, which often leads to death.

Klebsiella ozaenae affects the mucous membrane of the nose and paranasal sinuses, causing their atrophy, inflammation accompanied by the release of a viscous fetid secretion. K. rhinoscleromatis affects not only the mucous membrane of the nose, but also the trachea, bronchi, pharynx, larynx, while specific granulomas develop in the affected tissue with subsequent sclerosis and development of cartilaginous infiltrates. The course of the disease is chronic, death can occur due to obstruction of the trachea or larynx.

Post-infectious immunity is fragile and is mainly cellular in nature. In chronic disease, signs of GChZ sometimes develop.

Laboratory diagnostics of klebsiella

The main diagnostic method is bacteriological. The material for sowing may be different: pus, blood, cerebrospinal fluid, feces, washings from objects, etc. It is sown on the differential diagnostic medium K-2 (with urea, raffinose, bromothymol blue), after 24 hours large shiny mucous colonies with a color from yellow or green-yellow to blue grow. Then the bacteria are determined for mobility by sowing in Peshkov's medium and the presence of ornithine decarboxylase. These signs are not characteristic of Klebsiella. The final identification consists of studying the biochemical properties and determining the serogroup using the agglutination reaction of a live culture with K-sera. The isolated pure culture is tested for sensitivity to antibiotics.

Sometimes, an agglutination reaction or RSC with a standard O-Klebsiella antigen or with an autostrain can be used to diagnose Klebsiella. A fourfold increase in antibody titers is of diagnostic value.

Treatment of klebsiellosis

Treatment of Klebsiella according to clinical indications is carried out in a hospital setting. Antibiotics are not indicated for intestinal lesions. In case of dehydration (the presence of enterotoxin in the pathogen), saline solutions are administered orally or parenterally. In generalized and sluggish chronic forms, antibiotics are used (according to the results of sensitivity testing), autovaccines; measures are taken to stimulate immunity (autohemotherapy, pyrogen therapy, etc.).

How to prevent klebsiella?

Specific prevention of klebsiella has not been developed. General prevention comes down to strict adherence to sanitary and hygienic standards when storing food products, strict adherence to asepsis and antisepsis in medical institutions, and adherence to personal hygiene rules.