Kingella kingae

Kingella kingae
Scientific classification
Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Betaproteobacteria
Order:	Neisseriales
Family:	Neisseriaceae
Genus:	Kingella
Species:	kingae

Kingella kingae is a species of gram-negative aerobic coccobacilli. First isolated in 1960, it was not until the 1990s that culture techniques improved enough for it to become recognized as a significant cause of infection in young children. It is best known as a cause of septic arthritis, osteomyelitis, spondylodiscitis, bacteraemia, and endocarditis, and less frequently lower respiratory tract infections and meningitis.^[1]

K. kingae is part of the bacterial flora of the throat in young children and is transmitted from child-to-child. When it causes disease, the clinical presentation is often subtle and preceded by a recent history of stomatitis or upper respiratory infection.

One notable exception is in cases of endocarditis (heart valve infection), which can be more refractory to treatment. K. kingae is the fifth member of the HACEK group of fastidious gram-negative bacteria that cause endocarditis. Routine laboratory tests may be normal because the organism is difficult to culture. Inoculating the fluid from infected joints directly into blood culture vials can enhance the chances of an accurate culture, but extended culture times are not helpful.^[2]

The organism has also been known as Moraxella kingae.

K. kingae is oxidase-positive, catalase-negative, and beta-hemolytic.

Mechanism of Infection

Kingella kingae is thought to begin infection by colonizing the pharynx, crossing the epithelium by using an RTX toxin, and entering the circulation and reaching deeper tissues, such as bones and joints.

K. kingae express type IV pili which allow for enhanced adhesion to respiratory epithelial and synovial cells and thus increased likelihood of colonization. These pili have also been shown to be reduced in number as pathogenesis progresses. σ54 regulates the transcription of pilA1, a major pilus subunit. PilS and PilR, regulatory transcription factors best known from the Pseudomonas aeruginosa pilus system, also may regulate pilA expression. High levels of type IV pili on K.kingae are associated with spreading/corroding colony types, while low levels of type IV pili are associated with nonspreading/non-corroding colony types of K.kingae. ^[3] There are, in fact, three different types of populations: spreading/corroding (with high-density pilation, nonspreading/noncorroding colonies (low density pilation), and domed colonies (no pilation, and thus no adherence to epithelium). Generally, respiratory and nonendocarditis infections tend to be highly piliated, while joint fluid, bone, and endocarditis blood isolates are less piliated, if at all. ^[4]

Spondylodiscitis

Children under three years of age may become infected with K.kingae and develop Spondylodiscitis. Typical Symptoms include back pain, abdominal pain, and damage to the bones and joints. It generally targets the lumbar region of the spinal cord, and the only true way of diagnosing it is through biopsy or needle aspiration, as blood plate growth gives many false negatives. ^[5]

Osteomyelitis

Osteomyelitis occurs in previously healthy children. The infection rate is poorly documented, thus the illness tends to go underdiagnosed. K. kingae can be transmitted person to person in rare cases. Diagnostic tools include low-grade fever, elevated inflammatory markers (ESR and CRP), and / but white blood cell counts are generally unreliable since they vary among infected patients. K. kingae infections are generally comcomitant with upper respiratory diseases or stomatitis, since disrupted respiratory or buccal mucosa is likely to facilitate bacterial invasion and hematogenous dissemination.

The cause of osteoarticular infections is frequently not identified. Less than 15% of K. kingae-positive clinical specimens reveal organisms on Gram stain. Risk of misidentification to other more commonly diagnosed bacterium.^[6] Fortunately, K. kingae readily treatable with a wide variety of antibiotics such as beta-lactams, tetracyclines, erythromycin, and fluoroquinolones ^[7]. It shows low mininum inhibitory concentration (MIC) for penicillins, rifampicin, and azithromycin. Multiple studies have shown that inoculating synovial fluid or bone samples directly into blood culture bottles substantially increases the detection of K kingae compared with direct plating of specimens on solid media.

As an oropharyngeal colonizer, K kingae is transmitted respiratory secretions, saliva, and potentially oral contact with contaminated objects. Recent studies suggest K. kingae strains may demonstrate varying degrees of pathogenicity, which could support the person-to-person transfer of pathogenic K. kingae.

Infection has been shown to have high prevalence in the autumn and winter months.^[8]

Adult Infections

K.kingae infections are quite rare in adults, but they do occur in immunocompromised patients. Poor oral hygiene, pharyngitis, and mucosal ulceration are also predisposing factors for infection. The infection can occur in the respiratory or urinary tract, as it is a part of the normal flora in those two areas, and will develop into septicemia or septic arthritis. ^[9]

References

1. ^ Yagupsky P. Kingella kingae: from medical rarity to an emerging paediatric pathogen. Lancet Infectious Disease 2004 Jun;4(6):358-67.
2. ^ Petti CA; Bhally HS; Weinstein MP; Joho K; Wakefield T; Reller LB; Carroll KC. Utility of extended blood culture incubation for isolation of haemophilus, actinobacillus, cardiobacterium, eikenella, and kingella organisms: a retrospective multicenter evaluation. Journal of Clinical Microbiology. 2006 Jan;44(1):257-9.
3. ^ Kehl-Fie, T.E. et al (2009) Expression of Kingella kingae Type IV Pili Is Regulated by σ54, PilS, and PilR. J. Bacteriol. 191(15): 4976-86.
4. ^ Kehl-Fie, T.E. et al. (2010) Examination of Type IV Pilus Expression and Pilus-Associated Phenotypes in Kingella kingae Clinical Isolates. Infect Immun. 78(4): 1692-9.
5. ^ Ceroni, D. et al. (2010) Kingella kingae spondylodiscitis in young children: toward a new approach for bacteriological investigations? A preliminary report. J Child Orthop. 4(2):173-175.
6. ^ Kiang, K.M. et al. (2005) Outbreak of Osteomyelitis/Septic Arthritis Caused by Kingella kingae Among Child Care Center Attendees. Pediatrics. 116(2): e206-13.
7. ^ Petti CA; Bhally HS; Weinstein MP; Joho K; Wakefield T; Reller LB; Carroll KC. Utility of extended blood culture incubation for isolation of haemophilus, actinobacillus, cardiobacterium, eikenella, and kingella organisms: a retrospective multicenter evaluation. Journal of Clinical Microbiology. 2006 Jan;44(1):257-9.
8. ^ Kiang, K.M. et al. (2005) Outbreak of Osteomyelitis/Septic Arthritis Caused by Kingella kingae Among Child Care Center Attendees. Pediatrics. 116(2): e206-13.
9. ^ Ramana, K.V. and Mohanty, S.K. (2009) An adult case of urinary tract infection with Kingella kingae: a case report. J Med Case Reports. 3: 7236.