Infectious Disease and Microbiology – Kingella Species

Overview

Kingella species are Gram-negative coccobacilli that are part of the normal human oropharyngeal flora and can cause endogenous invasive infections. The most clinically important species is Kingella kingae, particularly in young children, where it is an important cause of bacteremia, septic arthritis, and osteomyelitis.

Kingella species are included in the HACEK group of fastidious Gram-negative organisms associated with infective endocarditis.

Important Species

The source lists:

• Kingella denitrificans

• Kingella kingae

Among these, K. kingae is the major human pathogen.

Microbiologic Characteristics

Kingella species are:

• Gram-negative coccobacilli

• Facultatively anaerobic

• Fastidious organisms

• Commonly associated with the upper respiratory tract

• Members of the HACEK group

Although the source lists both aerobic and facultatively anaerobic characteristics, the key practical point is that these are fastidious facultative Gram-negative organisms.

HACEK Association

The HACEK group includes:

H – Haemophilus and related organisms

A – Aggregatibacter

C – Cardiobacterium

E – Eikenella

K – Kingella

These organisms are classically associated with:

Subacute infective endocarditis

Incubation Period

The incubation period is:

Unknown

Because many infections arise from colonizing organisms already present in the upper respiratory tract, there may not be a clearly defined exposure-to-disease interval.

Epidemiology

Kingella infection is usually:

Endogenous

The organism may colonize the:

• Oropharynx

• Upper respiratory tract

Disease can occur when the organism enters the bloodstream and disseminates to distant sites.

Age Association

Kingella kingae is especially important in:

Infants and young children

It is a major cause of invasive osteoarticular infection in children, particularly in the preschool age group.

Bacteremia

Bacteremia occurs particularly in:

Children

It may be transient or associated with focal infection such as:

• Septic arthritis

• Osteomyelitis

• Endocarditis

Septic Arthritis

K. kingae is a well-recognized cause of:

Septic arthritis in young children

Commonly affected joints include large joints such as:

• Hip

• Knee

• Ankle

The illness may be less toxic or dramatic than septic arthritis caused by more aggressive organisms such as Staphylococcus aureus.

Osteomyelitis

Kingella kingae can also cause:

Osteomyelitis

This is particularly important in young children with:

• Limping

• Refusal to walk

• Localized bone pain

• Mild fever

• Elevated inflammatory markers

Clinical findings may be relatively subtle.

Osteoarticular Disease Pattern

A high-yield pattern is:

Young child

• ●

Mild fever

• ●

Limp or refusal to bear weight

• ●

Septic arthritis or osteomyelitis

→ Think Kingella kingae

Endocarditis

As a member of the HACEK group, Kingella can cause:

Infective endocarditis

This may have a:

• Subacute course

• Prolonged fever

• New or changing murmur

• Persistent bacteremia

• Embolic complications

HACEK Endocarditis Pattern

Fastidious Gram-negative organism

• ●

Subacute endocarditis

• ●

Oropharyngeal flora

→ Consider a HACEK organism, including Kingella

Normal Flora and Pathogenesis

Because Kingella can be part of normal human flora, infection often begins with:

Oropharyngeal colonization

followed by:

Mucosal invasion

then:

Bacteremia

and finally:

Seeding of bone, joint, or cardiac tissue

Suttonella indologenes

The source notes that:

Suttonella indologenes

was previously called:

Kingella indologenes

This organism has been associated with:

Eye infections

It is taxonomically distinct from the clinically important K. kingae.

Diagnosis

The source lists:

Culture

as the primary diagnostic method.

Culture Considerations

Kingella species can be fastidious, so routine culture may occasionally be difficult.

For suspected osteoarticular infection, specimens may include:

• Blood cultures

• Synovial fluid

• Bone aspirate

• Tissue specimens

Molecular Diagnosis

In modern practice, PCR-based testing can improve detection of K. kingae, particularly in children with suspected bone or joint infection when standard cultures are negative.

This is especially useful because the organism may be present in low numbers and may grow slowly.

Treatment

The source recommends:

Penicillin G combined with an aminoglycoside

This reflects an older treatment approach, especially for endocarditis.

Modern Treatment Considerations

For many Kingella infections, treatment is generally based on a:

Beta-lactam antibiotic

depending on susceptibility and infection site.

Potential agents may include:

• Penicillin derivatives

• Ampicillin

• Cephalosporins

For severe invasive disease or endocarditis, therapy should be guided by susceptibility testing and specialist recommendations.

Endocarditis Therapy

Historically, HACEK endocarditis was often treated with:

Penicillin + aminoglycoside

However, modern practice more commonly favors effective third-generation cephalosporins or other active beta-lactams, depending on susceptibility and local guidance.

High-Yield Clinical Pattern – Child

Preschool child

• ●

Limp/refusal to walk

• ●

Septic arthritis or osteomyelitis

• ●

Relatively mild systemic illness

→ Think Kingella kingae

High-Yield Clinical Pattern – Endocarditis

Subacute endocarditis

• ●

Fastidious Gram-negative coccobacillus

• ●

HACEK organism

→ Consider Kingella

Kingella vs. Other HACEK Organisms

Kingella

→ Young children

→ Septic arthritis

→ Osteomyelitis

→ Endocarditis

Aggregatibacter

→ Endocarditis

→ Oral flora

Cardiobacterium

→ Endocarditis

Eikenella

→ Human bite wounds

→ Oral flora

→ Endocarditis

Exam Essentials

Genus: Kingella

Important species: K. kingae

Morphology: Gram-negative coccobacillus

Metabolism: Facultatively anaerobic

Normal habitat: Oropharyngeal flora

HACEK member: Yes

Incubation: Unknown

Transmission/pathogenesis: Usually endogenous

Major pediatric disease: Septic arthritis and osteomyelitis

Bacteremia: More common in children

Endocarditis: Important HACEK manifestation

Diagnosis: Culture; PCR may improve detection

Historical treatment: Penicillin G + aminoglycoside

Modern principle: Susceptibility-guided beta-lactam therapy

Former Kingella species: Kingella indologenes → Suttonella indologenes

Key clinical pearl: Kingella kingae is a HACEK Gram-negative coccobacillus and an important cause of septic arthritis, osteomyelitis, and bacteremia in young children. A preschool child with a limp or refusal to bear weight and relatively mild systemic symptoms should prompt consideration of K. kingae.