Kingella

Kingella is a genus of Gram-negative bacteria in the family Neisseriaceae. The genus includes several species, of which Kingella kingae is the most medically important. These organisms are small, nonmotile coccobacilli that commonly occur in pairs and short chains and are oxidase positive.

Habitat and culture: Kingella species are part of the normal human oropharyngeal and upper respiratory flora, especially in children. They are fastidious and may be slow-growing on routine media. They can grow on blood agar and chocolate agar under CO2-enriched conditions, producing small, convex colonies. Identification can be challenging with conventional biochemical tests and is often aided by MALDI-TOF mass spectrometry or molecular methods; misidentification as Neisseria or Moraxella can occur.

Clinical relevance: The best known pathogenic species is K. kingae, a leading cause of septic arthritis and osteomyelitis in children aged six months to four years. It can also cause bacteremia and, rarely, endocarditis. In adults, invasive disease is uncommon. Transmission occurs via close contact and respiratory droplets following oropharyngeal colonization.

Pathogenesis and treatment: Virulence is associated with adherence and invasion of musculoskeletal tissues, with an RTX toxin (encoded by rtxA) described as a virulence factor. Treatments usually involve beta-lactam antibiotics such as penicillin or ampicillin, or third-generation cephalosporins, guided by susceptibility data. Resistance is uncommon but has been reported in a minority of isolates.

Diagnosis and epidemiology: Diagnosis relies on culture of sterile sites or detection by PCR from joint fluid, blood, or synovial tissue. Colonization rates are age-dependent and higher in children; disease occurrence varies by geography and study.