Kingella

Morphology and structural features

Bacteria of the genus Kingella, named after the prominent bacteriologist Elizabeth King, are classical Gram-negative microorganisms. Under a light microscope, they appear as small straight bacilli approximately 1 micrometer in length. A characteristic morphological feature is the shape of their poles—the ends of the bacteria may be gently rounded or have a specific "square-profiled" shape.

In microscopic smears, these bacteria are predominantly arranged in pairs or form very short chains. Kingellae do not form protective spores and lack capsules. Although they lack classical flagella, making them non-motile in the traditional sense, they possess specialized fimbriae (pili). These surface structures not only ensure reliable adhesion to host cells, but also allow bacteria to perform a specific "jerking" movement commonly referred to in microbiology as twitching motility.

Cultural and biochemical properties

In terms of respiration, kingellae are aerobes or facultative anaerobes, though the most active growth and reproduction occur specifically under aerobic conditions. These are fastidious microorganisms: they grow extremely poorly on simple nutrient media and critically require the addition of animal-derived factors for optimal cultivation. When plated on blood agar, they form a distinct zone of β-hemolysis around the colonies.

An interesting feature of kingellae is their ability to dissociate, forming two distinct colony types:

• R-forms (rough): characterized by a flat structure, the ability to actively spread across the surface, and cause characteristic agar corrosion. This property is directly linked to the presence of bacterial fimbriae and their motility.
• S-forms (smooth): have a regular convex shape, are completely devoid of fimbriae, and are entirely non-motile.

Biochemically, representatives of this genus have low metabolic activity: their enzymatic activity is very weakly expressed. Nevertheless, under laboratory conditions, they yield a consistently positive oxidase test and possess a somatic O-antigen in their antigenic structure.

Clinical significance and virulence factors

Under normal conditions, kingellae are habitual members of our body's microflora, colonizing the mucous membranes of the oropharynx and nasopharynx. Their latent pathogenic potential is primarily revealed in individuals with pronounced immunosuppression, making the infections they cause characteristically opportunistic. Among the three known species, Kingella kingae holds the greatest clinical and epidemiological significance.

Key virulence factors include bacterial endotoxin and the aforementioned fimbriae, which ensure firm attachment to affected tissues. The infectious process can manifest as severe systemic conditions: purulent meningitis, destructive arthritis, and osteomyelitis. A particularly vulnerable risk group comprises patients with implanted prosthetic heart valves—in this category of patients, K. kingae can cause severe infective endocarditis.

Diagnostics, treatment, and resistance

Kingellae exhibit extremely low resistance to aggressive environmental factors. They perish very rapidly upon heating—exposure to a temperature of 45 °C destroys the culture in just 10–15 minutes. Furthermore, they demonstrate high susceptibility to most standard antiseptic agents.

The primary method for reliable laboratory diagnosis of the infection is classical bacteriological culture. Depending on the suspected localization of the pathological process, blood, cerebrospinal fluid (CSF), or synovial fluid may be used as the clinical material under investigation.

Specific prophylaxis (vaccination) against these infections has not been developed to date. Therapy is entirely based on the pathogen's high intrinsic susceptibility to antibacterial drugs: first-line agents are β-lactams (such as penicillin and ampicillin), as well as macrolide antibiotics (e.g., erythromycin).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Adhesion mechanisms of bacteria belonging to the family Neisseriaceae
• Features of twitching motility
• Pathogenesis of infective endocarditis involving prosthetic valves
• The process of bacterial dissociation into R- and S-forms
• The role of endotoxin in the development of Gram-negative sepsis

Other topics in the section «Gram-negative aerobic rods (Pertussis, Brucella, Tularemia, Legionella, Coxiella/Q fever, Bartonella, Pseudomonas, Burkholderia, Acinetobacter, etc.)»

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.