Epidemiological features of invasive Kingella kingae infections and respiratory carriage of the organism

Evolving Approach to Antibiotic Treatment of Pediatric Spondylodiscitis

OBJECTIVE

To describe for intervertebral spondylodiscitis (IS) its clinical characteristics, treatment approaches with intravenous (IV) antibiotics, and clinical implications of changes in treatment approach.

STUDY DESIGN

This retrospective study included all children aged 0-18 years diagnosed with imaging-confirmed thoracic and lumbar IS from 2000 to 2022 at a tertiary pediatric hospital. Patients with longer IV treatment regimen were compared with those with a shorter clinically directed IV to oral regimen.

RESULTS

In all, 124 cases were included with median age 14.9 months (IQR, 12.7-19.4 months) at diagnosis. Irritability and pain while changing diapers were common symptoms (52.4% and 49.2%, respectively). Elevated erythrocyte sedimentation rate (ESR) was the most common laboratory finding (95%; median, 50 mm/h [IQR 34-64 mm/h]). Elevated erythrocyte sedimentation rate was found in higher proportions (95%) compared with elevated C-reactive protein (76%; median, 1.8 mg/dL; P < .001). Since implementing the shorter clinically directed IV treatment duration for patients with thoracic and lumbar IS, hospitalization duration was decreased from a median of 12 to 8 days (P = .008) and IV treatment duration by a median of 14 to 8 days (P < .001). Only 1 patient (1.6%) in the clinically directed treatment group required rehospitalization owing to failure of therapy. Conversely, 9 of 124 children in the cohort suffered from IV treatment-related complications; all had been treated IV for prolonged periods.

CONCLUSIONS

Early transition to oral treatment in pediatric spondylodiscitis seems to be appropriate clinically and shortens hospital stay and IV treatment duration without major negative clinical impact.

The Seasonality of Childhood Bone and Joint Infection with Focus on Kingella kingae: A Systematic Review

BACKGROUND

Seasonal trends in hospitalization for childhood bone and joint infection (BJI) are reported inconsistently. True seasonal variation would suggest an element of disease risk from environmental factors. This review evaluates all reported seasonal variations in childhood BJI, with additional analysis of seasonal trends for diseases secondary to Kingella kingae.

METHODS

A systematic review of the literature was undertaken from January 1, 1980, to August 1, 2024. Data were extracted on the hospitalization rate by season and/or month. Pathogen-specific studies for BJI secondary to K. kingae were examined separately.

RESULTS

Twenty studies met inclusion criteria encompassing 35,279 cases of childhood BJI. Most studies reported seasonal variation (n = 15, 75%). Eight studies specifically considered disease secondary to K. kingae, and all reported more frequent hospitalization in autumn and/or winter. This is in keeping with the role of respiratory pathogens and seasonal viruses in disease etiology for K. kingae BJI. Findings from other studies on the seasonality of childhood BJI were inconsistent. There were reported seasonal peaks in autumn/winter (4 studies), summer/spring (5 studies), or no variation (5 studies). Where microbiologic data were available, Staphylococcus aureus was the primary pathogen. The quality assessment demonstrated confounding and heterogeneous inclusion criteria affecting the seasonal analysis.

CONCLUSION

For childhood BJI caused by K. kingae, there appears to be a higher risk of hospitalization in autumn and/or winter months. This may relate to the seasonal circulation of respiratory viruses. There is currently insufficient evidence to support other forms of seasonal variation. Reported findings are likely affected by regional disease and pathogen characteristics.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Phylogenomic analysis of the understudied Neisseriaceae species reveals a poly- and paraphyletic Kingella genus

IMPORTANCE

Understanding the evolutionary relationships between the species in the Neisseriaceae family has been a persistent challenge in bacterial systematics due to high recombination rates in these species. Previous studies of this family have focused on Neisseria meningitidis and N. gonorrhoeae. However, previously understudied Neisseriaceae species are gaining new attention, with Kingella kingae now recognized as a common human pathogen and with Alysiella and Simonsiella being unique in the bacterial world as multicellular organisms. A better understanding of the genomic evolution of the Neisseriaceae can lead to the identification of specific genes and traits that underlie the remarkable diversity of this family.

Pediatric Osteoarticular Kingella kingae Infections of the Hand and Wrist: A Retrospective Study

Our understanding of pediatric osteoarticular infections (OAIs) has improved significantly in recent decades. Kingella kingae is now recognized as the most common pathogen responsible for OAIs in pediatric populations younger than 4 years old. Research has provided a better understanding of the specific types, clinical characteristics, biological repercussions, and functional outcomes of these infections. Hands and wrists are rarely infected, with few reports available in the literature. The present study aimed to examine this specific condition in a large patient cohort, explore the implications for each anatomical area using magnetic resonance imaging (MRI), and critically evaluate the evolution of therapeutic management.

Kingella kingae RtxA toxin interacts with sialylated gangliosides

The membrane-damaging RTX family cytotoxin RtxA is a key virulence factor of the emerging pediatric pathogen Kingella kingae, but little is known about the mechanism of RtxA binding to host cells. While we have previously shown that RtxA binds cell surface glycoproteins, here we demonstrate that the toxin also binds different types of gangliosides. The recognition of gangliosides by RtxA depended on sialic acid side groups of ganglioside glycans. Moreover, binding of RtxA to epithelial cells was significantly decreased in the presence of free sialylated gangliosides, which inhibited cytotoxic activity of the toxin. These results suggest that RtxA utilizes sialylated gangliosides as ubiquitous cell membrane receptor molecules on host cells to exert its cytotoxic action and support K. kingae infection.

Clinical and Biologic Characteristics of Kingella kingae -Induced Septic Arthritis of the Knee in Young Children

BACKGROUND AND OBJECTIVES

Septic arthritis of the knee is presumed to be the most frequent form of Kingella kingae -induced osteoarticular infection. This study aimed to report on the clinical course, biological parameters, and results of microbiological investigations among children with K. kingae -induced septic arthritis of the knee. It also assessed the modified Kocher-Caird criteria's ability to predict K. kingae -induced septic arthritis of the knee.

METHODS

The medical charts of 51 children below 4 years old with confirmed or highly probable K. kingae -induced arthritis of the knee were reviewed. Data were gathered on the five variables in the commonly-used Kocher-Caird prediction algorithm (body temperature, refusal to bear weight, leukocytosis, erythrocyte sedimentation rate, and C-reactive protein level).

RESULTS

Patients with K. kingae -induced arthritis of the knee usually presented with a mildly abnormal clinical picture and normal or near-normal serum levels of acute-phase reactants. Data on all five variables were available for all the children: 7 children had zero predictors; 8, 20, 12, and 4 children had 1, 2, 3, and 4 predictors, respectively; no children had 5 predictors. This gave an average of 1.96 predictive factors and a subsequent probability of ≤ 62.4% of infectious arthritis in this pediatric cohort.

CONCLUSIONS

Because the clinical features of K. kingae -induced arthritis of the knee overlap with many other conditions affecting this joint, the Kocher-Caird prediction algorithm is not sensitive enough to effectively detect K. kingae -induced septic arthritis of the knee. Excluding K. kingae -induced arthritis of the knee requires performing nucleic acid amplification assays on oropharyngeal swabs and joint fluid from those young children presenting with effusion of the knee, even in the absence of fever, leukocytosis, or a high Kocher-Caird score.

The Kingella kingae PilC1 MIDAS Motif Is Essential for Type IV Pilus Adhesive Activity and Twitching Motility

Kingella kingae is an emerging pathogen that has recently been identified as a leading cause of osteoarticular infections in young children. Colonization with K. kingae is common, with approximately 10% of young children carrying this organism in the oropharynx at any given time. Adherence to epithelial cells represents the first step in K. kingae colonization of the oropharynx, a prerequisite for invasive disease. Type IV pili and the pilus-associated PilC1 and PilC2 proteins have been shown to mediate K. kingae adherence to epithelial cells, but the molecular mechanism of this adhesion has remained unknown. Metal ion-dependent adhesion site (MIDAS) motifs are commonly found in integrins, where they function to promote an adhesive interaction with a ligand. In this study, we identified a potential MIDAS motif in K. kingae PilC1 which we hypothesized was directly involved in mediating type IV pilus adhesive interactions. We found that the K. kingae PilC1 MIDAS motif was required for bacterial adherence to epithelial cell monolayers and extracellular matrix proteins and for twitching motility. Our results demonstrate that K. kingae has co-opted a eukaryotic adhesive motif for promoting adherence to host structures and facilitating colonization.

Pharyngeal Colonization by Kingella kingae, Transmission, and Pathogenesis of Invasive Infections: A Narrative Review

With the appreciation of Kingella kingae as a prime etiology of osteoarticular infections in young children, there is an increasing interest in the pathogenesis of these diseases. The medical literature on K. kingae’s colonization and carriage was thoroughly reviewed. Kingella kingae colonizes the oropharynx after the second life semester, and its prevalence reaches 10% between the ages of 12 and 24 months, declining thereafter as children reach immunological maturity. Kingella kingae colonization is characterized by the periodic substitution of carried organisms by new strains. Whereas some strains frequently colonize asymptomatic children but are rarely isolated from diseased individuals, others are responsible for most invasive infections worldwide, indicating enhanced virulence. The colonized oropharyngeal mucosa is the source of child-to-child transmission, and daycare attendance is associated with a high carriage rate and increased risk of invasive disease. Kingella kingae elaborates a potent repeat-in-toxin (RTXA) that lyses epithelial, phagocytic, and synovial cells. This toxin breaches the epithelial barrier, facilitating bloodstream invasion and survival and the colonization of deep body tissues. Kingella kingae colonization and carriage play a crucial role in the person-to-person transmission of the bacterium, its dissemination in the community, and the pathogenesis of invasive infections.

Kingella kingae RtxA Cytotoxin in the Context of Other RTX Toxins

The Gram-negative bacterium Kingella kingae is part of the commensal oropharyngeal flora of young children. As detection methods have improved, K. kingae has been increasingly recognized as an emerging invasive pathogen that frequently causes skeletal system infections, bacteremia, and severe forms of infective endocarditis. K. kingae secretes an RtxA cytotoxin, which is involved in the development of clinical infection and belongs to an ever-growing family of cytolytic RTX (Repeats in ToXin) toxins secreted by Gram-negative pathogens. All RTX cytolysins share several characteristic structural features: (i) a hydrophobic pore-forming domain in the N-terminal part of the molecule; (ii) an acylated segment where the activation of the inactive protoxin to the toxin occurs by a co-expressed toxin-activating acyltransferase; (iii) a typical calcium-binding RTX domain in the C-terminal portion of the molecule with the characteristic glycine- and aspartate-rich nonapeptide repeats; and (iv) a C-proximal secretion signal recognized by the type I secretion system. RTX toxins, including RtxA from K. kingae, have been shown to act as highly efficient 'contact weapons' that penetrate and permeabilize host cell membranes and thus contribute to the pathogenesis of bacterial infections. RtxA was discovered relatively recently and the knowledge of its biological role remains limited. This review describes the structure and function of RtxA in the context of the most studied RTX toxins, the knowledge of which may contribute to a better understanding of the action of RtxA in the pathogenesis of K. kingae infections.

Primary Pyomyositis Caused by Kingella kingae in a 21-Month-old Infant: A Case Report

The authors report a rare case of an unusual primary pyomyositis of the biceps cruralis assigned to Kingella kingae in a 21-month-old girl. The reported case demonstrated that primary pyomyositis may be encountered during invasive infection due to K. kingae even if this manifestation remains rare. This bacterial etiology must, therefore, be evoked when a primary pyomyositis is observed, and this is in particular in children under 4 years of age.

Kingella kingae Osteoarticular Infections Approached through the Prism of the Pediatric Orthopedist

Nowadays, Kingella kingae (K. kingae) is considered as the main bacterial cause of osteoarticular infections (OAI) in children aged less than 48 months. Next to classical acute hematogenous osteomyelitis and septic arthritis, invasive K. kingae infections can also give rise to atypical osteoarticular infections, such as cellulitis, pyomyositis, bursitis, or tendon sheath infections. Clinically, K. kingae OAI are usually characterized by a mild clinical presentation and by a modest biologic inflammatory response to infection. Most of the time, children with skeletal system infections due to K. kingae would not require invasive surgical procedures, except maybe for excluding pyogenic germs' implication. In addition, K. kingae's OAI respond well even to short antibiotics treatments, and, therefore, the management of these infections requires only short hospitalization, and most of the patients can then be treated safely as outpatients.

The role of Kingella kingae in pre-school aged children with bone and joint infections

OBJECTIVES

The Pre-school Osteoarticular Infection (POI) study aimed to describe the burden of disease, epidemiology, microbiology and treatment of acute osteoarticular infections (OAI) and the role of Kingella kingae in these infections.

METHODS

Information about children 3-60 months of age who were hospitalized with an OAI to 11 different hospitals across Australia and New Zealand between January 2012 and December 2016 was collected retrospectively.

RESULTS

A total of 907 cases (73%) were included. Blood cultures grew a likely pathogen in only 18% (140/781). The peak age of presentation was 12 to 24 months (466/907, 51%) and Kingella kingae was the most frequently detected microorganism in this age group (60/466, 13%). In the majority of cases, no microorganism was detected (517/907, 57%). Addition of PCR to culture increased detection rates of K. kingae. However, PCR was performed infrequently (63/907, 7%).

CONCLUSIONS

This large multi-national study highlights the need for more widespread use of molecular diagnostic techniques for accurate microbiological diagnosis of OAI in pre-school aged children. The data from this study supports the hypothesis that a substantial proportion of pre-school aged children with OAI and no organism identified may in fact have undiagnosed K. kingae infection. Improved detection of Kingella cases is likely to reduce the average length of antimicrobial treatment.

Osteoarticular infection in children

AIMS

We aimed to describe the epidemiological, biological, and bacteriological characteristics of osteoarticular infections (OAIs) caused by Kingella kingae.

METHODS

The medical charts of all children presenting with OAIs to our institution over a 13-year period (January 2007 to December 2019) were reviewed. Among these patients, we extracted those which presented an OAI caused by K. kingae and their epidemiological data, biological results, and bacteriological aetiologies were assessed.

RESULTS

K. kingae was the main reported microorganism in our paediatric population, being responsible for 48.7% of OAIs confirmed bacteriologically. K. kingae affects primarily children aged between six months and 48 months. The highest prevalence of OAI caused by K. kingae was between seven months and 24 months old. After the patients were 27 months old, its incidence decreased significantly. The incidence though of infection throughout the year showed no significant differences. Three-quarters of patients with an OAI caused by K. kingae were afebrile at hospital admission, 11% had elevated WBCs, and 61.2% had abnormal CRPs, whereas the ESR was increased in 75%, constituting the most significant predictor of an OAI. On MRI, we noted 53% of arthritis affecting mostly the knee and 31% of osteomyelitis located primarily in the foot.

CONCLUSION

K. kingae should be recognized currently as the primary pathogen causing OAI in children younger than 48 months old. Diagnosis of an OAI caused by K. kingae is not always obvious, since this infection may occur with a mild-to-moderate clinical and biological inflammatory response. Extensive use of nucleic acid amplification assays improved the detection of fastidious pathogens and has increased the observed incidence of OAI, especially in children aged between six months and 48 months. We propose the incorporation of polymerase chain reaction assays into modern diagnostic algorithms for OAIs to better identify the bacteriological aetiology of OAIs. Cite this article: Bone Joint J 2021;103-B(3):578-583.

Kingella kingae Septic Arthritis in an Older-Than-Expected Child

Kingella kingae typically causes musculoskeletal infection in young children between the ages of 6 months and 4 years who may be in close contact with other similarly aged children who are colonized with the organism in their oropharynx. Kingella infections have rarely been described in older individuals with chronic medical conditions or immune compromise. This is a case report of a healthy, older child who developed an invasive infection due to Kingella kingae. Clinical and laboratory details are provided of an otherwise healthy 11-year-old female who developed an acute onset of septic arthritis of her shoulder. The organism was identified by culture and 16S polymerase chain reaction. Her clinical course necessitated an antibiotic change after the organism was correctly identified. The affected child had close contact with a 2-year-old sibling who recently had a viral upper respiratory infection. This case illustrates the potential for Kingella kingae to rarely cause invasive infection in older, healthy children. Supplemental laboratory techniques may be helpful to identify this organism. Although it is reasonable to limit the antibiotic spectrum for older children, clinicians should be aware of this possibility, particularly if there is a history of close contact with young children.

Kingella kingae as the Main Cause of Septic Arthritis: Importance of Molecular Diagnosis

BACKGROUND

Kingella kingae is an emergent pathogen causing septic arthritis (SA) in children.The objective of this study was to analyze the etiology of SA in children before and after the implementation of universal 16S rRNA gene polymerase chain reaction and sequencing (16SPCR) in synovial fluid.

METHODS

Children ≤14 years with acute SA from a Madrid cohort (2002-2013) were reviewed. Differences in etiology were analyzed before (period 1) and after (period 2) the implementation of bacterial 16SPCR in 2009. A comparison in epidemiology, clinical syndromes, therapy and outcome between infections caused by K. kingae and other bacteria was performed.

RESULTS

Bacteria were detected from 40/81 (49.4%) children, with a higher proportion of diagnosis after 16SPCR establishment (period 2, 63% vs. period 1, 31.4%; P = 0.005). The main etiologies were Staphylococcus aureus (37.5%) and K. kingae (35%), although K. kingae was the most common microorganism in P2 (48.3%). Children with K. kingae SA were less likely to be younger than 3 months (0 vs. 42.3%; P < 0.001), had less anemia (21.4 vs. 50%; P = 0.010), lower C-reactive protein (3.8 vs. 8.9 mg/dL; P = 0.039), less associated osteomyelitis (0 vs. 26.9%; P = 0.033), shorter intravenous therapy (6 vs. 15 days; P < 0.001), and had a nonsignificant lower rate of sequelae (0 vs. 30%; P = 0.15) than children with SA caused by other bacteria. However, they tended to have higher rate of fever (86 vs. 57%; P = 0.083).

CONCLUSIONS

K. kingae was frequently recovered in children with SA after the implementation of bacterial 16SPCR, producing a milder clinical syndrome and better outcome. Therefore, the use of molecular techniques may be important for the management of these children.

Cytotoxic activity of Kingella kingae RtxA toxin depends on post-translational acylation of lysine residues and cholesterol binding

Kingella kingae is a member of the commensal oropharyngeal flora of young children. Improvements in detection methods have led to the recognition of K. kingae as an emerging pathogen that frequently causes osteoarticular infections in children and a severe form of infective endocarditis in children and adults. Kingella kingae secretes a membrane-damaging RTX (Repeat in ToXin) toxin, RtxA, which is implicated in the development of clinical infections. However, the mechanism by which RtxA recognizes and kills host cells is largely unexplored. To facilitate structure-function studies of RtxA, we have developed a procedure for the overproduction and purification of milligram amounts of biologically active recombinant RtxA. Mass spectrometry analysis revealed the activation of RtxA by post-translational fatty acyl modification on the lysine residues 558 and/or 689 by the fatty-acyltransferase RtxC. Acylated RtxA was toxic to various human cells in a calcium-dependent manner and possessed pore-forming activity in planar lipid bilayers. Using various biochemical and biophysical approaches, we demonstrated that cholesterol facilitates the interaction of RtxA with artificial and cell membranes. The results of analyses using RtxA mutant variants suggested that the interaction between the toxin and cholesterol occurs via two cholesterol recognition/interaction amino acid consensus motifs located in the C-terminal portion of the pore-forming domain of the toxin. Based on our observations, we conclude that the cytotoxic activity of RtxA depends on post-translational acylation of the K558 and/or K689 residues and on the toxin binding to cholesterol in the membrane.

Temporal Association Between Rhinovirus Activity and Kingella kingae Osteoarticular Infections

OBJECTIVE

To determine whether the seasonal distribution of Kingella kingae osteoarticular infections is similar to that of common respiratory viruses.

STUDY DESIGN

Between October 2009 and September 2016, we extracted the results of K kingae-specific real-time polymerase chain reaction analyses performed for bone or joint specimens in patients from 2 pediatric tertiary care centers in Paris. We used data of respiratory virus detection from the Réseau National des Laboratoires network with coordination with the National Influenza Center of France. The Spearman rank correlation was used to assess a correlation between weekly distributions, with P < .05 denoting a significant correlation.

RESULTS

During the 7-year study period, 322 children were diagnosed with K kingae osteoarticular infection, and 317 testing episodes were K kingae-negative. We observed high activity for both K kingae osteoarticular infection and human rhinovirus (HRV) during the fall (98 [30.4%] and 2401 [39.1%] cases, respectively) and low activity during summer (59 [18.3%] and 681 [11.1%] cases, respectively). Weekly distributions of K kingae osteoarticular infection and rhinovirus activity were significantly correlated (r = 0.30; P = .03). In contrast, no significant correlation was found between the weekly distribution of K kingae osteoarticular infection and other respiratory viruses (r = -0.17, P = .34 compared with respiratory syncytial virus; r = -0.13, P = .34 compared with influenza virus; and r = -0.22, P = .11 compared with metapneumovirus).

CONCLUSION

A significant temporal association was observed between HRV circulation and K kingae osteoarticular infection, strengthening the hypothesis of a role of viral infections in the pathophysiology of K kingae invasive infection.

A transversal pilot study of oropharyngeal carriage of Kingella kingae in healthy children younger than 6 months

BACKGROUND

The aim of this pilot study was to investigate the extent of oropharyngeal Kingella kingae carriage during the first 6 months of life.

METHODS

We conducted a monocentric transversal pilot study on healthy children younger than 6 months in order to define the oropharyngeal carriage rate. Participants were recruited between December 2013 and September 2015 among children without symptoms or signs of invasive infections.

RESULTS

We demonstrated an oropharyngeal carriage rate of 0.67% in children younger than 6 months. Due to the really low carriage rate, it was not possible to draw statistically significant conclusion about any other characteristic of our population.

CONCLUSIONS

The present study suggests that the oropharyngeal carriage of Kingella kingae among a Swiss population of healthy infants younger than 6 months is exceptional. The scarcity of colonization and disease in the early months of life suggests thus that defense against mucosal carriage and invasive infection is above all provided by vertically acquired immunity. Limited exposure of the neonates due to limited social contacts may also represent another factor avoiding neonates' mucosal Kingella kingae carriage.

Defining the Mechanical Determinants of Kingella kingae Adherence to Host Cells

Kingella kingae is an important pathogen in young children and initiates infection by colonizing the posterior pharynx. Adherence to pharyngeal epithelial cells is an important first step in the process of colonization. In the present study, we sought to elucidate the interplay of type IV pili (T4P), a trimeric autotransporter adhesin called Knh, and the polysaccharide capsule in K. kingae adherence to host cells. Using adherence assays performed under shear stress, we observed that a strain expressing only Knh was capable of higher levels of adherence than a strain expressing only T4P. Using atomic force microscopy and transmission electron microscopy (TEM), we established that the capsule had a mean depth of 700 nm and that Knh was approximately 110 nm long. Using cationic ferritin capsule staining and thin-section transmission electron microscopy, we found that when bacteria expressing retractile T4P were in close contact with host cells, the capsule was absent at the point of contact between the bacterium and the host cell membrane. In a T4P retraction-deficient mutant, the capsule depth remained intact and adherence levels were markedly reduced. These results support the following model: T4P make initial contact with the host cell and mediate low-strength adherence. T4P retract, pulling the organism closer to the host cell and displacing the capsule, allowing Knh to be exposed and mediate high-strength, tight adherence to the host cell surface. This report provides the first description of the mechanical displacement of capsule enabling intimate bacterial adherence to host cells.IMPORTANCE Adherence to host cells is an important first step in bacterial colonization and pathogenicity. Kingella kingae has three surface factors that are involved in adherence: type IV pili (T4P), a trimeric autotransporter adhesin called Knh, and a polysaccharide capsule. Our results suggest that T4P mediate initial contact and low-strength adherence to host cells. T4P retraction draws the bacterium closer to the host cell and causes the displacement of capsule. This displacement exposes Knh and allows Knh to mediate high-strength adherence to the host cell. This work provides new insight into the interplay of T4P, a nonpilus adhesin, and a capsule and their effects on bacterial adherence to host cells.

Evaluation of dual target-specific real-time PCR for the detection of Kingella kingae in a Danish paediatric population

BACKGROUND

We aimed to evaluate the relevance of dual target real-time polymerase chain (PCR) assays targeting the rtxA and cpn60 genes of the paediatric pathogen Kingella kingae. We also studied for the first time the clinical and epidemiological features of K. kingae infections in a Danish population.

METHOD

Children with K. kingae-positive cultures were identified from 11,477 children and 86 children younger than 16 years old from whom blood cultures and joint fluid cultures were obtained between January 2010 and November 2016. Results were then compared to microbiological results obtained from 29 joint fluids (28 children) tested by dual target K. kingae real-time PCR from September 2014 to November 2016. Epidemiological data of all children with microbiologically confirmed K. kingae infections were collected.

RESULTS

From 2010 to 2016, we diagnosed 17 children with microbiological-proven K. kingae infections. During this period, blood cultures from five children and joint fluid cultures from a single child yielded K. kingae. Dual target K. kingae real-time PCR allowed us to increase the diagnostic yield of K. kingae infections by detecting the organism in 12 of 29 (41.4%) specimens. Notably, the 12 real-time PCR-positive specimens were rtxA-positive whereas only 10 (83.3%) were cpn60-positive. PCR-positive children were significantly younger than PCR-negative children (p-value: .01). A significant seasonal variation was found for patients with proven K. kingae infection (p-value: <.001), with a peak in autumn.

CONCLUSION

Dual target-specific real-time PCR markedly improved the detection of K. kingae in clinical specimens when compared to culture methods.

Septic Arthritis of Native Joints

Septic arthritis is a rheumatologic emergency that may lead to disability or death. Prompt evacuation of the joint, either by arthrocentesis at the bedside, open or arthroscopic drainage in the operating room, or imaging-guided drainage in the radiology suite, is mandatory. Methicillin-resistant Staphylococcus aureus (MRSA) has become a major cause of septic arthritis in the United States. MRSA joint infection seems to be associated with worse outcomes. Antibiotic courses of 3 to 4 weeks in duration are usually adequate for uncomplicated bacterial arthritis. Treatment duration should be extended to 6 weeks if there is imaging evidence of accompanying osteomyelitis.

The Type a and Type b Polysaccharide Capsules Predominate in an International Collection of Invasive Kingella kingae Isolates

Kingella kingae has emerged as a significant cause of septic arthritis, osteomyelitis, and bacteremia in young children. A recent study examining a diverse collection of K. kingae isolates from Israel revealed four different polysaccharide capsule types in this species, designated types a to d. To determine the global distribution of K. kingae capsule types, we assembled and capsule typed an international collection of K. kingae isolates. The findings reported here show that the type a and type b capsules represent >95% of the invasive isolates, similar to the Israeli isolate collection, suggesting that a polysaccharide-based vaccine targeting these two capsules could be an attractive approach to prevent K. kingae disease.

Kingella kingae is an encapsulated Gram-negative bacterium and an important etiology of osteoarticular infections in young children. A recent study examining a diverse collection of carrier and invasive K. kingae isolates from Israel revealed four distinct polysaccharide capsule types. In this study, to obtain a global view of K. kingae capsule type diversity, we examined an international collection of isolates using a multiplex PCR approach. The collection contained all four previously identified capsule types and no new capsule types. Over 95% of invasive isolates in the collection were type a or type b, similar to the findings in Israel. These results suggest that the type a and type b polysaccharide capsules may have enhanced pathogenic properties or may mark clonal groups of strains with specific virulence genes. In addition, they raise the possibility that a vaccine containing the type a and type b capsules might be an effective approach to preventing K. kingae disease.

IMPORTANCEKingella kingae has emerged as a significant cause of septic arthritis, osteomyelitis, and bacteremia in young children. A recent study examining a diverse collection of K. kingae isolates from Israel revealed four different polysaccharide capsule types in this species, designated types a to d. To determine the global distribution of K. kingae capsule types, we assembled and capsule typed an international collection of K. kingae isolates. The findings reported here show that the type a and type b capsules represent >95% of the invasive isolates, similar to the Israeli isolate collection, suggesting that a polysaccharide-based vaccine targeting these two capsules could be an attractive approach to prevent K. kingae disease.

In vitro characterization of biofilms formed by Kingella kingae

The Gram-negative bacterium Kingella kingae is part of the normal oropharyngeal mucosal flora of children <4 years old. K. kingae can enter the submucosa and cause infections of the skeletal system in children, including septic arthritis and osteomyelitis. The organism is also associated with infective endocarditis in children and adults. Although biofilm formation has been coupled with pharyngeal colonization, osteoarticular infections, and infective endocarditis, no studies have investigated biofilm formation in K. kingae. In this study we measured biofilm formation by 79 K. kingae clinical isolates using a 96-well microtiter plate crystal violet binding assay. We found that 37 of 79 strains (47%) formed biofilms. All strains that formed biofilms produced corroding colonies on agar. Biofilm formation was inhibited by proteinase K and DNase I. DNase I also caused the detachment of pre-formed K. kingae biofilm colonies. A mutant strain carrying a deletion of the pilus gene cluster pilA1pilA2fimB did not produce corroding colonies on agar, autoaggregate in broth, or form biofilms. Biofilm forming strains have higher levels of pilA1 expression. The extracellular components of biofilms contained 490 μg cm^-2 of protein, 0.68 μg cm^-2 of DNA, and 0.4 μg cm^-2 of total carbohydrates. We concluded that biofilm formation is common among K. kingae clinical isolates, and that biofilm formation is dependent on the production of proteinaceous pili and extracellular DNA. Biofilm development may have relevance to the colonization, transmission, and pathogenesis of this bacterium. Extracellular DNA production by K. kingae may facilitate horizontal gene transfer within the oral microbial community.

High rate of oropharyngeal Kingella kingae carriage in New Zealand children

AIM

This study aimed to describe the burden of disease and estimated rates of oropharyngeal carriage of Kingella kingae among New Zealand children. We compared polymerase chain reaction (PCR) and culture for the detection of this microorganism with a view to further development and implementation of K. kingae PCR in Christchurch Hospital.

METHODS

Oropharyngeal swabs from children between 6 and 48 months of age were analysed by culture to estimate carriage rates of K. kingae. Samples of a subgroup of children between 12 and 24 months of age were also tested by PCR. In addition, a retrospective review was performed on all cases of invasive K. kingae disease and children with osteoarticular infections.

RESULTS

Oropharyngeal cultures were positive for K. kingae in specimens from 4 out of 176 children (2.3%). PCR was significantly more sensitive and by PCR, the carriage rate rose to 22.9% (95% CI = 9.4-33.9%) (n = 48). From 2005 to 2015, 17 children between 6 and 48 months of age were identified with invasive infections due to K. kingae. Seventy-four children were found to have an osteoarticular infection. Most of these were culture-negative with a microbiological diagnosis made in only 15 cases (20.3%), only one due to K. kingae.

CONCLUSIONS

We found a very high carriage rate of K. kingae in New Zealand children and poor performance of K. kingae culture. It is likely that many cases of invasive K. kingae infections remain undetected. We recommend the use of a K. kingae PCR in all children under 4 years of age with a possible osteoarticular infection.

Identifying Reservoirs of Infections Caused by Kingella kingae: A Case-Control Study of Oropharyngeal Carriage of K. kingae Among Healthy Adults

BACKGROUND

Kingella kingae is currently recognized as a significant pathogen of the pediatric population. Nevertheless, the possibility for adults to serve as a reservoir of healthy carriers has not been studied.

METHOD

We conducted a monocentric transversal study on 228 healthy adults to define the carriage rate. Participants were recruited among the staff of a children's hospital, a population exposed to aerosolized droplets from children. A secondary analysis using a case-control method was conducted to assess risk factors for carriage.

RESULTS

We demonstrated an oropharyngeal carriage rate of 2.2% in this population. However, there was a striking similarity in the carriage rate among children younger than 4 years of age and adults living with children of that age group (8.8%). Use of day-care facilities for their own children was also demonstrated as a risk factor for adult carriage.

CONCLUSIONS

We were able to demonstrate the existence of adult carriage of K. kingae but our results point to transmission from children to adults. Our results do not allow us to conclude that professional exposure in a hospital setting is a risk factor for oropharyngeal carriage.

The Epidemiologic, Microbiologic and Clinical Picture of Bacteremia among Febrile Infants and Young Children Managed as Outpatients at the Emergency Room, before and after Initiation of the Routine Anti-Pneumococcal Immunization

We described the occult bacteremia (OB) and bacteremia with diagnosed focus (BwF) picture among children managed as outpatients at the pediatric emergency room (PER) in southern Israel, before and after the introduction of pneumococcal conjugate vaccines (PCVs) introduction in a retrospective study enrolling all three- to 36-month-old patients with fever >38.0 °C during 2005–2014. Of 511 (0.82% of all febrile patients) true bacteremias, 230 (45%) were managed as outpatients; 96 of 230 (41.7%) had OB and 134 (3.59%) had BwF. OB and BwF rates were 0.22% and 3.02%, respectively. A significant decrease was noted in OB and BwF rates (p = 0.0008 and p = 0.02, respectively). S. pneumoniae (SP, 37.5%), K. kingae (11.4%) and Brucella spp. (8.7%) were the most common OB pathogens and SP (29.8%), S. viridans (13.4%), and Brucella spp. (12.7%) were the most common in BwF patients. PCV13 serotypes were not found among the serotypes isolated post-PCV13 introduction. During 2010–2014 there was an increase in non-PCV13 serotype isolation (p = 0.005). SP was the main pathogen isolated among patients with pneumonia, acute otitis media (AOM) and periorbital cellulitis (62.5%, 33.3% and 60%, respectively). OB and BwF decreased following the introduction of PCVs and SP was the main pathogen in both conditions. Vaccine-SP serotypes were not isolated in OB after PCV13 introduction and non-vaccine serotypes increased significantly.

Pathogenesis of Kingella kingae Disease

The pathogenesis of Kingella kingae disease begins with colonization of the oropharynx, a process facilitated by type IV pili and a non-pilus trimeric autotransporter adhesin called Knh, factors that mediate adherence to respiratory epithelial cells. A potent RTX cytotoxin with broad cellular specificity may play a role in disrupting the epithelial barrier and facilitating invasion of the bloodstream, possibly in concert with a viral coinfection. Once in the bloodstream, the organism can disseminate to sites of invasive disease, primarily the joints, bones, and endocardium. Survival in the bloodstream and dissemination are likely aided by expression of a capsular polysaccharide and an exopolysaccharide galactan. The evidence for antigenic diversity of K. kingae surface exposed protein epitopes and the observation that type IV pili are selected against during invasive disease suggest that immune system pressure plays an important role in K. kingae pathogenicity.

Oropharyngeal Kingella kingae carriage in children: characteristics and correlation with osteoarticular infections

BACKGROUND

The aim of this study was to investigate changes in oropharyngeal K. kingae carriage during the first 4 y of life, including seasonal variation and comparison of asymptomatic carriage with cases of invasive osteoarticular infections (OAI).

METHODS

Oropharyngeal bacterial K. kingae carriage was screened in 744 healthy children aged 7-48 mo between January 2009 and December 2012. Oropharyngeal swabs were analyzed by rt-PCR targeting the DNA of K. kingae RTX toxin, epidemiological characteristics of asymptomatic carriers and OAI case patients were recorded.

RESULTS

The carriage prevalence showed no significant difference between age groups or seasons. Compared with asymptomatic carriers, OAI cases were more likely to be aged from 7 to 12 mo (OR = 2.5; 95% CI (1.2-5.0)) and 13-24 mo (OR = 2.2; 95% CI (1.2-3.9)), and less likely over 36 mo (OR = 0.2; 95% CI (0.1-0.7)). Fewer OAI cases were identified in spring compared to asymptomatic carriers (OR = 0.3; 95% CI (0.1-0.7)), while more were detected in autumn (OR = 2.5; 95% CI (1.4-4.4)).

CONCLUSION

Although oropharyngeal K. kingae colonization is a prerequisite for further invasive infection, this epidemiological study emphasizes that the carriage rate variations do not correlate with the variations of OAI incidence by gender, season, or age group.

Kingella kingae Causing Septic Arthritis of the Knee in an Immunocompetent Adult

The bacterium Kingella kingae is a species of Gram-negative coccobacillus usually found in the oropharynx. This is an emerging pathogen reported to cause bacteraemia, endocarditis, and osteoarticular infections in children and endocarditis in the immunocompromised adult. However, there are few cases of isolated joint infections reported in the immunocompetent adult. Due to specific isolation techniques required, delay in diagnosis can compromise patient outcome. We report a rare case of septic arthritis of the knee in an immunocompetent adult caused by K. kingae.

Kingella kingae: carriage, transmission, and disease

Kingella kingae is a common etiology of pediatric bacteremia and the leading agent of osteomyelitis and septic arthritis in children aged 6 to 36 months. This Gram-negative bacterium is carried asymptomatically in the oropharynx and disseminates by close interpersonal contact. The colonized epithelium is the source of bloodstream invasion and dissemination to distant sites, and certain clones show significant association with bacteremia, osteoarthritis, or endocarditis. Kingella kingae produces an RTX (repeat-in-toxin) toxin with broad-spectrum cytotoxicity that probably facilitates mucosal colonization and persistence of the organism in the bloodstream and deep body tissues. With the exception of patients with endocardial involvement, children with K. kingae diseases often show only mild symptoms and signs, necessitating clinical acumen. The isolation of K. kingae on routine solid media is suboptimal, and detection of the bacterium is significantly improved by inoculating exudates into blood culture bottles and the use of PCR-based assays. The organism is generally susceptible to antibiotics that are administered to young patients with joint and bone infections. β-Lactamase production is clonal, and the local prevalence of β-lactamase-producing strains is variable. If adequately and promptly treated, invasive K. kingae infections with no endocardial involvement usually run a benign clinical course.

First identification of a chromosomally located penicillinase gene in Kingella kingae species isolated in continental Europe

Kingella kingae is the major pathogen causing osteoarticular infections (OAI) in young children in numerous countries. Plasmid-borne TEM-1 penicillinase production has been sporadically detected in a few countries but not in continental Europe, despite a high prevalence of K. kingae infections. We describe here for the first time a K. kingae β-lactamase-producing strain in continental Europe and demonstrate the novel chromosomal location of the blaTEM-1 gene in K. kingae species.

Outbreaks of Kingella kingae infections in daycare facilities

During the past decade, transmission of the bacterium Kingella kingae has caused clusters of serious infections, including osteomyelitis, septic arthritis, bacteremia, endocarditis, and meningitis, among children in daycare centers in the United States, France, and Israel. These events have been characterized by high attack rates of disease and prevalence of the invasive strain among asymptomatic classmates of the respective index patients, suggesting that the causative organisms benefitted from enhanced colonization fitness, high transmissibility, and high virulence. After prophylactic antibacterial drugs were administered to close contacts of infected children, no further cases of disease were detected in the facilities, although test results showed that some children still carried the bacterium. Increased awareness of this public health problem and use of improved culture methods and sensitive nucleic acid amplification assays for detecting infected children and respiratory carriers are needed to identify and adequately investigate outbreaks of K. kingae disease.

RTX toxin plays a key role in Kingella kingae virulence in an infant rat model

Kingella kingae is a human oral bacterium that can cause diseases of the skeletal system in children and infective endocarditis in children and adults. K. kingae produces a toxin of the RTX group, RtxA. To investigate the role of RtxA in disease pathogenesis in vivo, K. kingae strain PYKK081 and its isogenic RtxA-deficient strain KKNB100 were tested for their virulence and pathological consequences upon intraperitoneal injections in 7-day-postnatal (PN 7) rats. At the doses above 8.0 × 10(6) cells/animal, PYKK081 was able to cause a fatal illness, resulting in rapid weight loss, bacteremia, and abdominal necrotic lesion formation. Significant histopathology was observed in thymus, spleen, and bone marrow. Strain KKNB100 was less toxic to animals. Neither weight loss, bacteremia, nor histopathological changes were evident. Animals injected with KKNB100 exhibited a significantly elevated circulating white blood cell (WBC) count, whereas animals injected with PYKK081 had a WBC count that resembled that of the uninfected control. This observation parallels the subtleties associated with clinical presentation of K. kingae disease in humans and suggests that the toxin contributes to WBC depletion. Thus, our results demonstrate that RtxA is a key K. kingae virulence factor. Furthermore, our findings suggest that the PN 7 rat can serve as a useful model for understanding disease caused by K. kingae and for elucidating diagnostic parameters in human patients.

Investigation of an outbreak of osteoarticular infections caused by Kingella kingae in a childcare center using molecular techniques

We describe an outbreak of 5 osteoarticular infections among 24 daycare center attendees. Polymerase chain reaction revealed Kingella kingae in the joint fluid of 1 child and in 85% of throat samples from healthy contacts. Multilocus sequence typing performed on the joint fluid and carriage isolates identified an unique sequence type. Rifampin failed to eradicate K. kingae carriage.

Comparing the oropharyngeal colonization density of Kingella kingae between asymptomatic carriers and children with invasive osteoarticular infections

Colonization of the oropharynx by Kingella kingae is currently considered to be a prerequisite for later development of invasive infections. However, the oropharyngeal K. kingae DNA bacterial load in children with osteoarticular infections caused by this microorganism is not different than that of asymptomatic carriers.

30 years of study of Kingella kingae: post tenebras, lux

Kingella kingae is a Gram-negative bacterium that is today recognized as the major cause of joint and bone infections in young children. This microorganism is a member of the normal flora of the oropharynx, and the carriage rate among children under 4 years of age is approximately 10%. K. kingae is transmitted from child to child through close personal contact. Key virulence factors of K. kingae include expression of type IV pili, Knh-mediated adhesive activity and production of a potent RTX toxin. The clinical presentation of K. kingae invasive infection is often subtle and may be associated to mild-to-moderate biologic inflammatory responses, highlighting the importance a high index of suspicion. Molecular diagnosis of K. kingae infections by nucleic acid amplification techniques enables identification of this fastidious microorganism. Invasive infections typically respond favorably to medical treatment, with the exception of cases of endocarditis, which may require urgent valve replacement.

Calcium binding properties of the Kingella kingae PilC1 and PilC2 proteins have differential effects on type IV pilus-mediated adherence and twitching motility

Kingella kingae is an emerging bacterial pathogen that is being recognized increasingly as an important etiology of septic arthritis, osteomyelitis, and bacteremia, especially in young children. The pathogenesis of K. kingae disease begins with bacterial adherence to respiratory epithelium, which is dependent on type IV pili and is influenced by two PilC-like proteins called PilC1 and PilC2. Production of either PilC1 or PilC2 is necessary for K. kingae piliation and bacterial adherence. In this study, we set out to further investigate the role of PilC1 and PilC2 in type IV pilus-associated phenotypes. We found that PilC1 contains a functional 9-amino-acid calcium-binding (Ca-binding) site with homology to the Pseudomonas aeruginosa PilY1 Ca-binding site and that PilC2 contains a functional 12-amino-acid Ca-binding site with homology to the human calmodulin Ca-binding site. Using targeted mutagenesis to disrupt the Ca-binding sites, we demonstrated that the PilC1 and PilC2 Ca-binding sites are dispensable for piliation. Interestingly, we showed that the PilC1 site is necessary for twitching motility and adherence to Chang epithelial cells, while the PilC2 site has only a minor influence on twitching motility and no influence on adherence. These findings establish key differences in PilC1 and PilC2 function in K. kingae and provide insights into the biology of the PilC-like family of proteins.

[Acute osteomyelitis: epidemiology, clinical manifestations, diagnosis and treatment]

BACKGROUND AND AIMS

The present study focuses on the epidemiology, clinical and laboratory data, and management of osteomyelitis in a pediatric third level hospital.

METHODOLOGY

All cases of children under 15 years-old admitted with osteomyelitis between 2000 and 2011 were retrospectively reviewed until July 2006, then prospectively from then until 2011.

RESULTS

A total of 50 patients were identified (52% males) with median age at diagnosis of 2 years. Principal onset manifestations were pain (94%), functional impairment (90%) and fever (72%). The femur (32%), fibula (28%) and calcaneus (22%) were most affected bones. Leucocytosis > 12.000/μl was found in 56%, elevated ESR > 20 mm/h in 26%, and elevated CRP > 20 mg/L in 64%. Blood culture was positive in 20%, with group A streptococcus being the most frequently isolated bacteria (11%). All diagnoses were confirmed by a (99)Tc scintigraphy bone scan. Antibiotic therapy was initially intravenously (mean time of administration: 10 days ± 3 SD), followed by oral medication (mean time of administration: 18 days ± 6 SD). Surgery was necessary in 3 patients. Evolution of all cases was excellent, despite 3 exceptions that resolved over time.

CONCLUSIONS

The current short-term intravenous therapy led to shorter hospitalizations. There were no statistically significant differences between time from clinical onset or in CRP levels at discharge compared to long-term therapies prior to 2006.

Modulation of Kingella kingae adherence to human epithelial cells by type IV Pili, capsule, and a novel trimeric autotransporter

Kingella kingae is an emerging bacterial pathogen that is being recognized increasingly as an important etiology of septic arthritis, osteomyelitis, and bacteremia, especially in young children. Colonization of the posterior pharynx is a key step in the pathogenesis of K. kingae disease. Previous work established that type IV pili are necessary for K. kingae adherence to the respiratory epithelium. In this study, we set out to identify additional factors that influence K. kingae interactions with human epithelial cells. We found that genetic disruption of the gene encoding a predicted trimeric autotransporter protein called Knh (Kingella NhhA homolog) resulted in reduced adherence to human epithelial cells. In addition, we established that K. kingae elaborates a surface-associated polysaccharide capsule that requires a predicted ABC-type transporter export operon called ctrABCD for surface presentation. Furthermore, we discovered that the presence of a surface capsule interferes with Knh-mediated adherence to human epithelial cells by nonpiliated organisms and that maximal adherence in the presence of a capsule requires the predicted type IV pilus retraction machinery, PilT/PilU. On the basis of the data presented here, we propose a novel adherence mechanism that allows K. kingae to adhere efficiently to human epithelial cells while remaining encapsulated and more resistant to immune clearance.

IMPORTANCE

Kingella kingae is a Gram-negative bacterium that is being recognized increasingly as a cause of joint and bone infections in young children. The pathogenesis of disease due to K. kingae begins with bacterial colonization of the upper respiratory tract, and previous work established that surface hair-like fibers called type IV pili are necessary for K. kingae adherence to respiratory epithelial cells. In this study, we set out to identify additional factors that influence K. kingae interactions with respiratory epithelial cells. We discovered a novel surface protein called Knh that mediates K. kingae adherence and found that a surface-associated carbohydrate capsule interferes with the Knh-mediated adherence of organisms lacking pili. Further analysis revealed that pilus retraction is necessary for maximal Knh-mediated adherence in the presence of the capsule. Our results may lead to new strategies to prevent disease due to K. kingae and potentially other pathogenic bacteria.

Small risk of osteoarticular infections in children with asymptomatic oropharyngeal carriage of Kingella kingae

The aim of this study was to evaluate the absolute risk for children younger than 4 years of age with asymptomatic oropharyngeal carriage of Kingella kingae to sustain an osteoarticular infection. The rate of K. kingae carriage in the oropharyngeal mucosa was 9% among healthy children, and the risk for an asymptomatic carrier to develop an osteoarticular infection due to K. Kingae was estimated to be lower than 1%.

Can early MRI distinguish between Kingella kingae and Gram-positive cocci in osteoarticular infections in young children?

BACKGROUND

K. kingae is a common causative organism in acute osteoarticular infections (OAIs) in children under 4 years of age. Differentiation between K. kingae and Gram-positive cocci (GPC) is of great interest therapeutically.

OBJECTIVE

Our aim was to identify early distinguishing MRI features of OAIs.

MATERIALS AND METHODS

Thirty-one children younger than 4 years of age with OAI underwent MRI at presentation. Of these, 21 were caused by K. kingae and ten by GPC. Bone and soft tissue reaction, epiphyseal cartilage involvement, bone and subperiosteal abscess formation were compared between the two groups. Interobserver agreement was measured.

RESULTS

Bone reaction was less frequent (P = 0.0066) and soft tissue reaction less severe (P = 0.0087) in the K. kingae group. Epiphysis cartilage abscesses were present only in the K. kingae group (P = 0.0118). No difference was found for bone abscess (P = 0.1411), subperiosteal abscess (P = 1) or joint effusion (P = 0.4414). Interobserver agreement was good for all criteria.

CONCLUSION

MRI is useful in differentiating K. kingae from GPC in OAI. Cartilaginous involvement and modest soft tissue and bone reaction suggest K. kingae.

Cytotoxic effects of Kingella kingae outer membrane vesicles on human cells

Kingella kingae is an emerging pathogen causing osteoarticular infections in pediatric patients. Electron microscopy of K. kingae clinical isolates revealed the heterogeneously-sized membranous structures blebbing from the outer membrane that were classified as outer membrane vesicles (OMVs). OMVs purified from the secreted fraction of a septic arthritis K. kingae isolate were characterized. Among several major proteins, K. kingae OMVs contained virulence factors RtxA toxin and PilC2 pilus adhesin. RtxA was also found secreted as a soluble protein in the extracellular environment indicating that the bacterium may utilize different mechanisms for the toxin delivery. OMVs were shown to be hemolytic and possess some leukotoxic activity while high leukotoxicity was detected in the non-hemolytic OMV-free component of the secreted fraction. OMVs were internalized by human osteoblasts and synovial cells. Upon interaction with OMVs, the cells produced increased levels of human granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 6 (IL-6) suggesting that these cytokines might be involved in the signaling response of infected joint and bone tissues during natural K. kingae infection. This study is the first report of OMV production by K. kingae and demonstrates that OMVs are a complex virulence factor of the organism causing cytolytic and inflammatory effects on host cells.

Kingella kingae: an emerging pathogen in young children

Kingella kingae is being recognized increasingly as a common etiology of pediatric osteoarticular infections, bacteremia, and endocarditis, which reflects improved culture methods and use of nucleic acid-amplification techniques in clinical microbiology laboratories. K kingae colonizes the posterior pharynx of young children and is transmitted from child to child through close personal contact. Day care attendance increases the risk for colonization and transmission, and clusters of K kingae infections among day care center attendees have been reported. Key virulence factors in K kingae include type IV pili and a potent RTX toxin. In previously healthy children, >95% of K kingae infections are diagnosed between the ages of 6 and 48 months. Among children with underlying medical conditions, K kingae disease may occur at older ages as well. The clinical presentation of K kingae disease is often subtle and may be associated with normal levels of acute-phase reactants, which underscores the importance of a high index of suspicion. K kingae is usually susceptible to ß-lactam antibiotics, and infections typically respond well to medical treatment, with the exception of cases of endocarditis.

Invasive pediatric Kingella kingae Infections: a nationwide collaborative study

BACKGROUND

Kingella kingae is a gram-negative coccobacillus, increasingly recognized as an invasive pediatric pathogen. To date, only few small series of invasive K. kingae infections have been published, mostly from single medical centers. A nationwide multicenter study was performed to investigate the epidemiologic, clinical, and laboratory features of children with culture-proven K. kingae infections.

METHODS

Clinical microbiology laboratories serving all 22 medical centers in Israel were contacted in a search for children aged 0 to 18 years from whom K. kingae was isolated from a normally sterile site, dating from as far back as possible until December 31, 2007. Medical records of identified patients were reviewed using uniform case definitions.

RESULTS

A total of 322 episodes of infection were identified in 321 children, of which 96% occurred before the age of 36 months. The annual incidence in children aged <4 years was 9.4 per 100,000. Infections showed a seasonal nadir between February and April. Skeletal system infections occurred in 169 (52.6%) children and included septic arthritis, osteomyelitis, and tenosynovitis. Occult bacteremia occurred in 140 children (43.6%), endocarditis in 8 (2.5%), and pneumonia in 4 (1.2%). With the exception of endocarditis cases, patients usually appeared only mildly ill. About one-quarter of children had a body temperature <38 degrees C, 57.1% had a blood white blood cell count <15,000/mm, 22.0% had normal C-reactive protein values, and 31.8% had nonelevated erythrocyte sedimentation rate.

CONCLUSIONS

K. kingae infections usually occur in otherwise healthy children aged 6 to 36 months, mainly causing skeletal system infections and bacteremia, and occasionally endocarditis and pneumonia. Clinical presentation is usually mild, except for endocarditis, necessitating a high index of suspicion.

Procession to pediatric bacteremia and sepsis: covert operations and failures in diplomacy

Despite advances in diagnosis and treatment, bacterial sepsis remains a major cause of pediatric morbidity and mortality, particularly among neonates, the critically ill, and the growing immunocompromised patient population. Sepsis is the end point of a complex and dynamic series of events in which both host and microbial factors drive high morbidity and potentially lethal physiologic alterations. In this article we provide a succinct overview of the events that lead to pediatric bloodstream infections (BSIs) and sepsis, with a focus on the molecular mechanisms used by bacteria to subvert host barriers and local immunity to gain access to and persist within the systemic circulation. In the events preceding and during BSI and sepsis, Gram-positive and Gram-negative pathogens use a battery of factors for translocation, inhibition of immunity, molecular mimicry, intracellular survival, and nutrient scavenging. Gaps in understanding the molecular pathogenesis of bacterial BSIs and sepsis are highlighted as opportunities to identify and develop new therapeutics.

Examination of type IV pilus expression and pilus-associated phenotypes in Kingella kingae clinical isolates

Kingella kingae is a gram-negative bacterium that is being recognized increasingly as a cause of septic arthritis and osteomyelitis in young children. Previous work established that K. kingae expresses type IV pili that mediate adherence to respiratory epithelial and synovial cells. PilA1 is the major pilus subunit in K. kingae type IV pili and is essential for pilus assembly. To develop a better understanding of the role of K. kingae type IV pili during colonization and invasive disease, we examined a collection of clinical isolates for pilus expression and in vitro adherence. In addition, in a subset of isolates we performed nucleotide sequencing to assess the level of conservation of PilA1. The majority of respiratory and nonendocarditis blood isolates were piliated, while the majority of joint fluid, bone, and endocarditis blood isolates were nonpiliated. The piliated isolates formed either spreading/corroding or nonspreading/noncorroding colonies and were uniformly adherent, while the nonpiliated isolates formed domed colonies and were nonadherent. PilA1 sequence varied significantly from strain to strain, resulting in substantial variability in antibody reactivity. These results suggest that type IV pili may confer a selective advantage on K. kingae early in infection and a selective disadvantage on K. kingae at later stages in the pathogenic process. We speculate that PilA1 is immunogenic during natural infection and undergoes antigenic variation to escape the immune response.

Dissemination of Kingella kingae in the community and long-term persistence of invasive clones

BACKGROUND

Although Kingella kingae is being increasingly recognized as an important pediatric pathogen, our current understanding of the transmission of the organism is limited. The dissemination of K. kingae in the community was studied in 2 ethnic groups living side-by-side in Southern Israel.

METHODS

Organisms recovered from oropharyngeal cultures, obtained from healthy young Jewish and Bedouin children during a 12-month period, were typed by pulsed-field gel electrophoresis and compared.

RESULTS

Isolates from Bedouin children usually differed from those derived from Jews, confirming the relative social isolation of the 2 populations and the importance of close mingling in the spread of K. kingae. Significant clustering of genotypic clones in households and Bedouin neighborhoods was observed, indicating person-to-person transmission through intimate contact. Organisms detected in the study were identical to historical isolates recovered over the last 15 years from respiratory carriers and patients with bacteremia or skeletal infections.

CONCLUSIONS

The present study demonstrates that children may be asymptomatically colonized in the respiratory tract by virulent K. kingae clones. The organism is transmitted from child-to-child through intimate contact. Some strains exhibit increased fitness and are maintained in the population for prolonged periods.

Expression of Kingella kingae type IV pili is regulated by sigma54, PilS, and PilR

Kingella kingae is a member of the Neisseriaceae and is being recognized increasingly as an important cause of serious disease in children. Recent work has demonstrated that K. kingae expresses type IV pili that mediate adherence to respiratory epithelial and synovial cells and are selected against during invasive disease. In the current study, we examined the genome of K. kingae strain 269-492 and identified homologs of the rpoN and the pilS and pilR genes that are essential for pilus expression in Pseudomonas aeruginosa but not in the pathogenic Neisseria species. The disruption of either rpoN or pilR in K. kingae resulted in a marked reduction in the level of transcript for the major pilus subunit (pilA1) and eliminated piliation. In contrast, the disruption of pilS resulted in only partial reduction in the level of pilA1 transcript and a partial decrease in piliation. Furthermore, the disruption of pilS in colony variants with high-density piliation resulted in variants with low-density piliation. Mutations in the promoter region of pilA1 and gel shift analysis demonstrated that both sigma(54) and PilR act directly at the pilA1 promoter, with PilR binding to two repetitive elements. These data suggest that the regulation of K. kingae type IV pilus expression is complex and multilayered, influenced by both the genetic state and environmental cues.

Molecular diagnosis of Kingella kingae osteoarticular infections by specific real-time PCR assay

Kingella kingae is an emerging pathogen that is recognized as a causative agent of septic arthritis and osteomyelitis, primarily in infants and children. The bacterium is best detected by rapid inoculation in blood culture systems or by real-time PCR assays. Pathogenesis of the agent was linked recently to the production of a potent cytotoxin, known as RTX, which is toxic to a variety of human cell types. The locus encoding the RTX toxin is thought to be a putative virulence factor, and is, apparently, essential for inducing cytotoxic effects on respiratory epithelial, synovial and macrophage-like cells. Herein, we describe a novel real-time PCR assay that targets the RTX toxin gene and illustrate its use in two clinical cases. The assay exhibited a sensitivity of 30 c.f.u., which is 10-fold more sensitive than a previously published semi-nested broad-range 16S rRNA gene PCR, and showed no cross-reactivity with several related species and common osteoarticular pathogens.