Infective Endocarditis Due to Kingella kingae

Infective endocarditis due to Kingella kingae is a rare but serious invasive infection that occurs mostly in children. Recent advances in nucleic acid amplification testing as well as in cardiac imaging have enabled more accurate diagnosis. A good understanding of the epidemiology and virulence factors remains crucial to guide the therapeutic approach. Here, we synthesize the current state of knowledge on epidemiological features, pathophysiological insights, complications, and therapy regarding Kingella kingae endocarditis in children and adults. Finally, throughout this comprehensive review, knowledge gaps and areas for future research are also identified.

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.

Acquisition, co-option, and duplication of the rtx toxin system and the emergence of virulence in Kingella

The bacterial genus Kingella includes two pathogenic species, namely Kingella kingae and Kingella negevensis, as well as strictly commensal species. Both K. kingae and K. negevensis secrete a toxin called RtxA that is absent in the commensal species. Here we present a phylogenomic study of the genus Kingella, including new genomic sequences for 88 clinical isolates, genotyping of another 131 global isolates, and analysis of 52 available genomes. The phylogenetic evidence supports that the toxin-encoding operon rtxCA was acquired by a common ancestor of the pathogenic Kingella species, and that a preexisting type-I secretion system was co-opted for toxin export. Subsequent genomic reorganization distributed the toxin machinery across two loci, with 30-35% of K. kingae strains containing two copies of the rtxA toxin gene. The rtxA duplication is largely clonal and is associated with invasive disease. Assays with isogenic strains show that a single copy of rtxA is associated with reduced cytotoxicity in vitro. Thus, our study identifies key steps in the evolutionary transition from commensal to pathogen, including horizontal gene transfer, co-option of an existing secretion system, and gene duplication.

Whole-Genome Sequencing Reveals Differences among Kingella kingae Strains from Carriers and Patients with Invasive Infections

As a result of the increasing use of sensitive nucleic acid amplification tests, Kingella kingae is being recognized as a common pathogen of early childhood, causing medical conditions ranging from asymptomatic oropharyngeal colonization to bacteremia, osteoarthritis, and life-threatening endocarditis. However, the genomic determinants associated with the different clinical outcomes are unknown. Employing whole-genome sequencing, we studied 125 international K. kingae isolates derived from 23 healthy carriers and 102 patients with invasive infections, including bacteremia (n = 23), osteoarthritis (n = 61), and endocarditis (n = 18). We compared their genomic structures and contents to identify genomic determinants associated with the different clinical conditions. The mean genome size of the strains was 2,024,228 bp, and the pangenome comprised 4,026 predicted genes, of which 1,460 (36.3%) were core genes shared by >99% of the isolates. No single gene discriminated between carried and invasive strains; however, 43 genes were significantly more frequent in invasive isolates, compared to asymptomatically carried organisms, and a few showed a significant differential distribution among isolates from skeletal system infections, bacteremia, and endocarditis. The gene encoding the iron-regulated protein FrpC was uniformly absent in all 18 endocarditis-associated strains but was present in one-third of other invasive isolates. Similar to other members of the Neisseriaceae family, the K. kingae differences in invasiveness and tropism for specific body tissues appear to depend on combinations of multiple virulence-associated determinants that are widely distributed throughout the genome. The potential role of the absence of the FrpC protein in the pathogenesis of endocardial invasion deserves further investigation. IMPORTANCE The wide range of clinical severities exhibited by invasive Kingella kingae infections strongly suggests that isolates differ in their genomic contents, and strains associated with life-threatening endocarditis may harbor distinct genomic determinants that result in cardiac tropism and severe tissue damage. The results of the present study show that no single gene discriminated between asymptomatically carried isolates and invasive strains. However, 43 putative genes were significantly more frequent among invasive isolates than among pharyngeal colonizers. In addition, several genes displayed a significant differential distribution among isolates from bacteremia, skeletal system infections, and endocarditis, suggesting that the virulence and tissue tropism of K. kingae are multifactorial and polygenic, depending on changes in the allele content and genomic organization. Further analysis of these putative genes may identify genomic determinants of the invasiveness of K. kingae and its affinity for specific body tissues and potential targets for a future protective vaccine.

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.

Kingella kingae and Viral Infections

Kingella kingae (K. kingae) is an oropharyngeal commensal agent of toddlers and the primary cause of osteoarticular infections in 6–23-month-old children. Knowing that the oropharynx of young children is the reservoir and the portal of entry of K. kingae, these results suggested that a viral infection may promote K. kingae infection. In this narrative review, we report the current knowledge of the concomitance between K. kingae and viral infections. This hypothesis was first suggested because some authors described that symptoms of viral infections were frequently concomitant with K. kingae infection. Second, specific viral syndromes, such as hand, foot and mouth disease or stomatitis, have been described in children experiencing a K. kingae infection. Moreover, some clusters of K. kingae infection occurring in daycare centers were preceded by viral outbreaks. Third, the major viruses identified in patients during K. kingae infection were human rhinovirus or coxsackievirus, which both belong to the Picornaviridae family and are known to facilitate bacterial infections. Finally, a temporal association was observed between human rhinovirus circulation and K. kingae infection. Although highly probable, the role of viral infection in the K. kingae pathophysiology remains unclear and is based on case description or temporal association. Molecular studies are needed.

Pathogenic determinants of Kingella kingae disease

Kingella kingae is an emerging pediatric pathogen and is increasingly recognized as a leading etiology of septic arthritis, osteomyelitis, and bacteremia and an occasional cause of endocarditis in young children. The pathogenesis of K. kingae disease begins with colonization of the upper respiratory tract followed by breach of the respiratory epithelial barrier and hematogenous spread to distant sites of infection, primarily the joints, bones, and endocardium. As recognition of K. kingae as a pathogen has increased, interest in defining the molecular determinants of K. kingae pathogenicity has grown. This effort has identified numerous bacterial surface factors that likely play key roles in the pathogenic process of K. kingae disease, including type IV pili and the Knh trimeric autotransporter (adherence to the host), a potent RTX-family toxin (epithelial barrier breach), and multiple surface polysaccharides (complement and neutrophil resistance). Herein, we review the current state of knowledge of each of these factors, providing insights into potential approaches to the prevention and/or treatment of K. kingae disease.

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.

Clinical Features and Comparison of Kingella and Non-Kingella Endocarditis in Children, Israel

Kingella spp. have emerged as an important cause of invasive pediatric diseases. Data on Kingella infective endocarditis (KIE) in children are scarce. We compared the clinical features of pediatric KIE cases with those of Streptococcus species IE (StIE) and Staphylococcus aureus IE (SaIE). A total of 60 patients were included in the study. Throughout the study period, a rise in incidence of KIE was noted. KIE patients were significantly younger than those with StIE and SaIE, were predominately boys, and had higher temperature at admission, history of oral aphthae before IE diagnosis, and higher lymphocyte count (p<0.05). Pediatric KIE exhibits unique features compared with StIE and SaIE. Therefore, in young healthy children <36 months of age, especially boys, with or without a congenital heart defect, with a recent history of oral aphthae, and experiencing signs and symptoms compatible with endocarditis, Kingella should be suspected as the causative pathogen.

Review highlights the latest research in Kingella kingae and stresses that molecular tests are required for diagnosis

AIM

The aim of this study was to provide an update on paediatric Kingella kingae infections.

METHODS

We used the PubMed database to identify studies published in English, French and Spanish up to 15 November 2020.

RESULTS

Kingella kingae colonised the oropharynx after the age of 6 months, and the mucosal surface was the portal of entry of the organism to the bloodstream and the source of child-to-child spread. Attending day care centres was associated with increased carriage rate and transmission and disease outbreaks were detected in day care facilities. Skeletal system infections were usually characterised by mild symptoms and moderately elevated inflammation markers, requiring a high clinical suspicion index. The organism was difficult to recover in cultures and molecular tests significantly improve its detection. Kingella kingae was generally susceptible to beta-lactam antibiotics, and skeletal diseases and bacteraemia responded to antimicrobial, leaving no long-term sequelae. However, patients with endocarditis frequently experienced life-threatening complications and the case fatality rate exceeded 10%.

CONCLUSION

Kingella kingae was the prime aetiology of skeletal system infections in children aged 6-48 months. Paediatricians should be aware of the peculiar features of this infection and the need to use molecular tests for diagnosis.

Outbreaks of Kingella kingae Infections in Daycare Centers Suggest Tissue Tropism of the Causative Strains

BACKGROUND

Although Kingella kingae is recognized as an important pediatric pathogen, our knowledge of the virulence factors involved in the invasion of specific host's tissues is limited. Outbreaks of K kingae infections in daycare centers represent natural experiments in which a single virulent strain, introduced into a cohort of susceptible young children, causes multiple infections. If K kingae strains exhibit tissue tropism, the syndromes observed in a given cluster of cases would be relatively homogeneous.

METHODS

Clinical data of all the K kingae outbreaks known to date were gathered and analyzed. The clinical syndromes diagnosed in the affected attendees were classified as septic arthritis, osteomyelitis, tenosynovitis, soft tissue infection, bacteremia with no focal disease, endocarditis, and meningitis, and computed separately. To assess the similarity of the clinical syndromes detected within outbreaks, we used the Cramer V statistic, which is a measure of the association between 2 nominal variables and, for the purposes of the study, between the detected clinical syndromes and the outbreaks.

RESULTS

A total of 23 outbreaks involving 61 attendees were identified. The mean±SD attack rate in the affected classrooms was 15.8% ± 4.8%, and the K kingae colonization rate among the attendees was 54.8% ± 25.3%. Seventy-two separate foci of infection were diagnosed. Osteomyelitis and septic arthritis were the most common clinical syndromes and were diagnosed in 26 children each, followed by tenosynovitis in 4 children. The clinical syndromes diagnosed among attendees to the same classroom showed a statistically significant tendency to be similar (P = .015).

CONCLUSIONS

The distribution of clinical syndromes in clusters of K kingae infections differs from that of sporadic cases. The causative strains combine enhanced virulence and high transmissibility, and show tropism toward bones, joints, and tendon sheaths. This information can be used to identify virulence factors associated with invasion of these specific host tissues.

Invasive infection from Kingella kingae: Not only arthritis

Kingella kingae is a known pathogen for osteoarticular infections in young children. However other invasive infections such as pneumonia in immunocompetent patients are scarcely described in literature. We present an unusual case of bacteremia and lower respiratory tract infection in a previously healthy infant, the first one described in Greek pediatric population. The pathogen was identified using both culture and molecular techniques

Virulence determinants of the emerging pathogen Kingella kingae

Kingella kingae is a gram-negative coccobacillus that is a fastidious commensal organism in the oropharynx and is being recognized increasingly as a common cause of osteoarticular infections and other invasive diseases in young children. The pathogenesis of K. kingae disease begins with bacterial adherence to respiratory epithelium, followed by translocation across the epithelial barrier, survival in the bloodstream, and dissemination to distant sites, including bones, joints, and the endocardium, among others. Characterization of the determinants of K. kingae pathogenicity has revealed a novel model of adherence that involves the interplay of type IV pili, a non-pilus adhesin, and a polysaccharide capsule and a novel model of resistance to serum killing and neutrophil killing that involves complementary functions of a polysaccharide capsule and an exopolysaccharide. These models likely apply to other bacterial pathogens as well.

Recurrent Acute Septic Arthritis Caused by Kingella kingae in a 16-Month-Old Boy

We describe the first case of 2 consecutive acute septic arthritis infections of both knees caused by the same virulent strain of Kingella kingae belonging to the virulent sequence type complex 14, in a 16-month-old boy. Both infections occurred after viral upper respiratory tract infections.

On King Saul, Two Missing Mules, and Kingella kingae: The Serendipitous Discovery of a Pediatric Pathogen

For the first 2 decades following Kingella kingae's initial characterization, this fastidious organism was considered an unusual cause of human infection until a study published in 1992 reported that inoculation of synovial fluid aspirates into blood culture vials improved the recovery of the bacterium. The authors of the original publication report herein the history of the discovery and review the progress made in the research of the organism.

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.

Detection of Respiratory Colonization by Kingella kingae and the Novel Kingella negevensis Species in Children: Uses and Methodology

The recognition of the role of Kingella kingae as one of the main etiologic agents of skeletal system infections in young children and the recent discovery of the novel Kingella negevensis species have resulted in an increasing interest in these two emerging pediatric pathogens. Both bacteria colonize the oropharynx and are not detected in nasopharyngeal specimens, and the colonized mucosal surface is their portal of entry to the bloodstream. Although species-specific nucleic acid amplification assays have significantly improved the detection of kingellae and facilitated patients' management, the increasing use of this diagnostic approach has the potential drawback of neglecting culture recovery of these organisms. The isolation of Kingella species enables the thorough genotyping of strains for epidemiological purposes, the study of the dynamics of asymptomatic colonization and person-to-person transmission, the investigation of the pathogenesis of invasive infections, and the determination of antibiotic susceptibility patterns. The culture isolation of pharyngeal strains and their comparison with isolates derived from normally sterile body sites may also aid in identifying virulence factors involved in the transition from colonization to invasive disease which could represent potential targets for a future protective vaccine. The two species are notoriously fastidious, and their isolation from upper respiratory tract specimens requires a short transport time, plating on selective vancomycin-containing blood-agar medium, and incubation under capnophilic and aerobic conditions. The identification of K. kingae and K. negevensis can be performed by a combination of the typical Gram stain and biochemical tests and confirmed and differentiated by molecular assays that target the groEL and mdh genes.

A New Highly Sensitive and Specific Real-Time PCR Assay Targeting the Malate Dehydrogenase Gene of Kingella kingae and Application to 201 Pediatric Clinical Specimens

Kingella kingae is a significant pediatric pathogen responsible for bone and joint infections, occult bacteremia, and endocarditis in early childhood. Past efforts to detect this bacterium using culture and broad-range 16S rRNA gene PCR assays from clinical specimens have proven unsatisfactory; therefore, by the late 2000s, these were gradually phased out to explore the benefits of specific real-time PCR tests targeting the groEL gene and the RTX locus of K. kingae However, recent studies showed that real-time PCR (RT-PCR) assays targeting the Kingella sp. RTX locus that are currently available for the diagnosis of K. kingae infection lack specificity because they could not distinguish between K. kingae and the recently described Kingella negevensis species. Furthermore, in silico analysis of the groEL gene from a large collection of 45 K. kingae strains showed that primers and probes from K. kingaegroEL-based RT-PCR assays display a few mismatches with K. kingae groEL variations that may result in decreased detection sensitivity, especially in paucibacillary clinical specimens. In order to provide an alternative to groEL- and RTX-targeting RT-PCR assays that may suffer from suboptimal specificity and sensitivity, a K. kingae-specific RT-PCR assay targeting the malate dehydrogenase (mdh) gene was developed for predicting no mismatch between primers and probe and 18 variants of the K. kingae mdh gene from 20 distinct sequence types of K. kingae This novel K. kingae-specific RT-PCR assay demonstrated high specificity and sensitivity and was successfully used to diagnose K. kingae infections and carriage in 104 clinical specimens from children between 7 months and 7 years old.

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.

Isolation and characterization of Kingella negevensis sp. nov., a novel Kingella species detected in a healthy paediatric population

We herein report the isolation and characterization of 21 Gram-stain-negative strains cultivated from the oropharynx of healthy children in Israel and Switzerland. Initially described as small colony variants of Kingella kingae, phenotypic analysis, biochemical analysis, phylogenetic analysis based on sequencing of the partial 16S rRNA gene and five housekeeping genes (abcZ, adk, G6PD, groEL and recA), and whole genome sequencing and comparison between members of the genera Kingella and Neisseria provided evidence for assigning them to the genus Kingella. Cellular fatty acids included important amounts of C12 : 0, C14 : 0, C16 : 0 and C16 : 1n7. Digital DNA-DNA hybridization between the isolates Sch538T and K. kingae ATCC 23330T revealed relatedness of 19.9 %. Comparative analysis of 16S rRNA gene sequences available in GenBank allowed matches to strains isolated in the USA, suggesting a wider geographical distribution. A novel species named Kingella negevensis sp. nov. is proposed, as most strains have been isolated in the Negev, a desert region of southern Israel. The type strain is Sch538T (=CCUG 69806T=CSUR P957).

Investigation of Kingella kingae Invasive Infection Outbreaks in Day Care Facilities: Assessment of a Rapid Genotyping Tool Targeting the DNA Uptake Sequence

Outbreaks of Kingella kingae invasive infections have recently been reported in day care centers. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) revealed that although the invasive strains had widespread dissemination in the day care population, less virulent strains were also circulating in the facilities. However, these typing tools are costly, time-consuming, and labor-intensive and provide delayed results. A study was conducted to assess the performance of a rapid and cost-effective genotyping tool targeting the DNA uptake sequence (DUS) in the investigation of outbreaks of K. kingae disease. DUS typing (DUST) patterns of each strain from 7 different clusters were compared to distinguish genotypically linked strains from others. PFGE and, when available, MLST results were used as gold standards. DUST was assessed on 80 K. kingae isolates from Nir-Itzhak (n = 14), Tel-Nof (n = 14), Palmahim (n = 5), Umm-al-Fahm (n = 7), Eilat (n = 8), Nevatim (n = 15) in Israel and Paris, France (n = 17). A unique DUST pattern was involved in the Nir-Itzhak, Palmahim, Umm-al-Fahm, and Paris episodes. Two DUST patterns were found in Eilat, whereas at least 3 were identified in the Tel-Nof and Nevatim episodes. In total, 11 (13.8%) children carried a K. kingae isolate that differed from the outbreak strain. These results were concordant with those obtained with the traditional PFGE and MLST methods. DUST appears to be sensitive and specific in distinguishing the invasive outbreak strain from others in asymptomatic carriers and could be useful to limit unnecessary exposure of the entire day care population to selective antibiotic pressure.

An Outbreak of Kingella Kingae Infections Complicating a Severe Hand, Foot, And Mouth Disease Outbreak in Nice, France, 2016

We report the investigation methods for the diagnosis of an epidemic and culture-negative Kingella kingae endocarditis complicating a severe outbreak of hand, foot and mouth disease in a childcare center. The diagnosis was confirmed by polymerase chain reaction testing performed from cardiac tissue. Our findings argue for the systematic investigation of K. kingae outbreaks by using molecular tools in such context.

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.

Geme JW. Kingella kingae Expresses Four Structurally Distinct Polysaccharide Capsules That Differ in Their Correlation with Invasive Disease

Kingella kingae is an encapsulated gram-negative organism that is a common cause of osteoarticular infections in young children. In earlier work, we identified a glycosyltransferase gene called csaA that is necessary for synthesis of the [3)-β-GalpNAc-(1→5)-β-Kdop-(2→] polysaccharide capsule (type a) in K. kingae strain 269-492. In the current study, we analyzed a large collection of invasive and carrier isolates from Israel and found that csaA was present in only 47% of the isolates. Further examination of this collection using primers based on the sequence that flanks csaA revealed three additional gene clusters (designated the csb, csc, and csd loci), all encoding predicted glycosyltransferases. The csb locus contains the csbA, csbB, and csbC genes and is associated with a capsule that is a polymer of [6)-α-GlcpNAc-(1→5)-β-(8-OAc)Kdop-(2→] (type b). The csc locus contains the cscA, cscB, and cscC genes and is associated with a capsule that is a polymer of [3)-β-Ribf-(1→2)-β-Ribf-(1→2)-β-Ribf-(1→4)-β-Kdop-(2→] (type c). The csd locus contains the csdA, csdB, and csdC genes and is associated with a capsule that is a polymer of [P-(O→3)[β-Galp-(1→4)]-β-GlcpNAc-(1→3)-α-GlcpNAc-1-] (type d). Introduction of the csa, csb, csc, and csd loci into strain KK01Δcsa, a strain 269-492 derivative that lacks the native csaA gene, was sufficient to produce the type a capsule, type b capsule, type c capsule, and type d capsule, respectively, indicating that these loci are solely responsible for determining capsule type in K. kingae. Further analysis demonstrated that 96% of the invasive isolates express either the type a or type b capsule and that a disproportionate percentage of carrier isolates express the type c or type d capsule. These results establish that there are at least four structurally distinct K. kingae capsule types and suggest that capsule type plays an important role in promoting K. kingae invasive disease.

Patterns of Kingella kingae Disease Outbreaks

BACKGROUND

Kingella kingae outbreaks occur sporadically in childcare centers but remain poorly understood and difficult to identify.

METHODS

To provide the basis of a better knowledge of K. kingae outbreaks patterns that may help to guide identification and management strategies, we collected epidemiological, clinical and laboratory data from all reported K. kingae outbreaks, and those from 2 new Israel outbreaks in 2014.

RESULTS

Nine outbreaks were identified in the USA, Israel and France from 2003 to 2014. Twenty-seven children with a median age of 14 ± 4.1 months were affected, male:female ratio of 1.4:1. Outbreaks demonstrated seasonal patterns from the 10th to the 45th weeks, a mean duration of 13.1 ± 8.4 days, a mean attack rate of 17.3 ± 5.1% and a case-fatality rate of 3.7% (1/27). Seventy-four percentage of children had fever (20/27), and the mean values of white blood cell count and C-reactive protein level were 14.6 ± 4.5 × 10/L and 23.8 ± 24.1 mg/L, respectively. Osteoarticular infections accounted for 88.9% of cases (24/27), bacteremia 7.4% (2/27), endocarditis 3.7% (1/27) and meningitis 3.7% (1/27). Specific real-time polymerase chain reaction demonstrated higher performance than culture methods in the diagnosis of case patients and investigations of oropharyngeal K. kingae carriage among close contacts, and multilocus sequence typing methods revealed that ST-6 and ST-25 invasive strains were responsible for multiple country-dependent outbreaks. Coviral infections were identified in the majority of K. kingae outbreaks, notably those causing oral ulcers.

CONCLUSIONS

K. kingae outbreaks displayed severe K. kingae diseases that were poorly confirmed with culture methods. We argue for the use of genomic technologies to investigate further K. kingae outbreaks.

Outbreaks of Invasive Kingella kingae Infections in Closed Communities

OBJECTIVES

To describe the results of the epidemiologic investigation of outbreaks of invasive Kingella kingae infections among attendees at daycare facilities located in 4 closed communities in Israel.

STUDY DESIGN

The preschool-aged population of communities with clusters of Kingella cases had oropharyngeal cultures performed. K kingae isolates from infected patients and healthy contacts were genotyped by pulsed field gel electrophoresis to determine the spread of outbreak strains.

RESULTS

The affected closed communities (3 military bases and 1 "kibbutz" commune) were characterized by tight social and family networks and intensive mingling. The outbreaks affected 9 of 51 attendees (attack rate: 17.6%) age 8-19 months (median: 12 months), within a 21-day period. Cases included skeletal system infections (n = 8) and bacteremia (n = 1); K kingae isolates were confirmed by the use of blood culture vials and selective media. Clinical presentation was mild and acute-phase reactants were usually normal or only moderately elevated. Thirty out of 55 (54.5%) asymptomatic children carried the outbreak strains. Analysis of the 3 clusters in which the entire preschool-aged population was cultured revealed that 31 of 71 (43.7%) children younger than 24 months of age were colonized with K kingae organisms compared with 8 of 105 (7.6%) older children (P < .001).

CONCLUSIONS

Clusters of invasive K kingae infections characterized by sudden onset, high attack rate, and wide dissemination of the outbreak strain can occur in daycare facilities and closed communities. Because the mild clinical presentation of invasive K kingae infections and the fastidious nature of the organism, a high index of suspicion and use of sensitive detection methods are recommended.

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 infections in children

BACKGROUND

Improvements in culture techniques and molecular detection methods have led to findings indicating that, particularly in infants and young children, Kingella kingae is a significantly more important pathogen than previously thought. However, despite this, the pediatric community is still largely unaware of the existence of this organism. The aim of this review is therefore to summarise current knowledge of the epidemiology, transmission, clinical presentation, diagnosis and treatment of K. kingae infections in children.

DISCUSSION

K. kingae is a common coloniser of the oropharynx, can be transmitted from child to child, and can cause outbreaks of infection. Invasive infections almost exclusively occur in children aged between six months and four years of age, and involve mainly joints and bone, less frequently the endocardium, and very rarely other localisations. With the exception of bacteremia and endocarditis, which can be followed by severe complications, the diseases due to K. kingae are usually accompanied by mild to moderate clinical signs and symptoms, and only slightly altered laboratory data. Moreover, they generally respond to widely used antibiotics, although resistant strains are reported. However, the mild symptoms and limited increase in the levels of acute phase reactants create problems because K. kingae disease may be confused with other clinical conditions that have a similar clinical picture.

CONCLUSIONS

Although K. kingae was identified more than 50 years ago, it is poorly known by pediatricians and is not systematically sought in laboratories. Education is therefore necessary in order to reduce the risk of outbreaks, permit the early identification of K. kingae infections, and allow the prompt prescription of adequate therapeutic regimens capable of avoiding the risk of a negative evolution in those cases in which this elusive pathogen can cause significant clinical problems.

The bacterial pangenome as a new tool for analysing pathogenic bacteria

The bacterial pangenome was introduced in 2005 and, in recent years, has been the subject of many studies. Thanks to progress in next-generation sequencing methods, the pangenome can be divided into two parts, the core (common to the studied strains) and the accessory genome, offering a large panel of uses. In this review, we have presented the analysis methods, the pangenome composition and its application as a study of lifestyle. We have also shown that the pangenome may be used as a new tool for redefining the pathogenic species. We applied this to the Escherichia coli and Shigella species, which have been a subject of controversy regarding their taxonomic and pathogenic position.

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Pangenome is a new way of studying pathogenic bacteria.

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Pangenome can be used as a taxonomic tool.

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This review describes pangenome in the world of pathogenic bacteria.

Kingella kingae sequence type-complex 14 arthritis in a 16-month-old child in Greece

We describe the first case of Kingella kingae arthritis in a 16-month-old girl in Greece, which has been diagnosed by novel molecular techniques. A joint aspiration of her knee was performed before the initiation of antibiotics, as well as on the 5th and 14th day of empiric antimicrobial therapy. The synovial fluid white blood cell count decreased from 65,000 to 1500 cells/mm, but the percentage of neutrophils remained 90% in all 3 specimens. Molecular analysis of the synovial fluid specimens by real-time polymerase chain reaction and multilocus sequence typing enabled us to reveal the presence of K. kingae belonging to the international sequence type-complex 14, which persisted up to the fifth day of antibiotic therapy.

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.

Kingella kingae KK247, an Atypical Pulsed-Field Gel Electrophoresis Clone A Strain

Kingella kingae strain KK247 was isolated from an adult Israeli patient with endocarditis. It belongs to pulsed-field gel electrophoresis clone A, has a 2,113,021-bp genome, a 15,507-bp plasmid that carries genes encoding β-lactamases, and possesses 45 transposases, compared to the 5 detected in other K. kingae strains.

Major intercontinentally distributed sequence types of Kingella kingae and development of a rapid molecular typing tool

Although Kingella kingae is the most common etiology of osteoarticular infections in young children, is a frequent cause of bacteremia in those younger than 4 years, and has been involved in clusters of invasive infections among daycare center attendees, the population structure of the species has not been systematically studied. Using multilocus sequence typing, we investigated the genetic diversity of the largest intercontinental collection of K. kingae strains to date. To facilitate typing of bacterial isolates, we developed a novel genotyping tool that targets the DNA uptake sequence (DUS). Among 324 strains isolated from asymptomatic carriers and patients from Israel, Europe, North America, and Australia with various invasive forms of the disease from 1960 to 2013, we identified 64 sequence types (STs) and 12 ST complexes (STcs). Five predominant STcs, comprising 72.2% of all strains, were distributed intercontinentally. ST-6 was the most frequent, showing a worldwide distribution, and appeared genotypically isolated by exhibiting few neighboring STs, suggesting an optimal fitness. ST-14 and ST-23 appeared to be the oldest groups of bacteria, while ST-25 probably emerged more recently from the highly evolutive ST-23. Using the DUS typing method, randomly chosen isolates were correctly classified to one of the major STcs. The comprehensive description of K. kingae evolution would help to detect new emerging clones and decipher virulence and fitness mechanisms. The rapid and reproducible DUS typing method may serve in the initial investigation of K. kingae outbreaks.

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.

High rates of complications following Kingella kingae infective endocarditis in children: a case series and review of the literature

Kingella kingae is part of the Haemophilus spp., Aggregatibacter spp., Cardiobacterium hominis, Eikenella corrodens and Kingella spp. organisms that are known to cause bacterial endocarditis. Evidence suggests it is also a common pharyngeal colonizer in children <2 years of age. We reviewed the literature to determine common complications of K. kingae infective endocarditis in children.

Genotyping, local prevalence and international dissemination of β-lactamase-producing Kingella kingae strains

β-lactamase production has been sporadically reported in the emerging Kingella kingae pathogen but the phenomenon has not been studied in-depth. We investigated the prevalence of β-lactamase production among K. kingae isolates from different geographical origins and genetically characterized β-lactamase-producing strains. Seven hundred and seventy-eight isolates from Iceland, the USA, France, Israel, Spain and Canada were screened for β-lactamase production and, if positive, were characterized by PFGE and MLST genotyping, as well as rtxA, por, blaTEM and 16S rRNA sequencing. β-lactamase was identified in invasive strains from Iceland (n=4/14, 28.6%), the USA (n=3/15, 20.0%) and Israel (n=2/190, 1.1%) and in carriage strains in the USA (n=5/17, 29.4%) and Israel (n=66/429, 15.4%). No French, Spanish or Canadian isolates were β-lactamase producers. Among β-lactamase producers, a perfect congruency between the different typing methods was observed. Surprisingly, all US and Icelandic β-lactamase-producing isolates were almost indistinguishable, belonged to the major international invasive PFGE clone K/MLST ST-6, but differed from the four genetically unrelated Israeli β-lactamase-producing clones. Representative strains of different genotypes produced the TEM-1 enzyme. K. kingae β-lactamase producers exhibit a clear clonal distribution and have dissimilar invasive potential. The presence of the enzyme in isolates belonging to the major worldwide invasive clone K/ST-6 highlights the possible spread of β-lactam resistance, and emphasizes the importance of routine testing of all K. kingae clinical isolates for β-lactamase production.

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.

A prospective study of intrafamilial oropharyngeal transmission of Kingella kingae

To evaluate the intrafamilial oropharyngeal transmission of Kingella kingae, we conducted a prospective study among pairs of siblings. We found that 55% of children who suffered from osteoarticular infections due to K. kingae, and 40% of asymptomatic carriers of K. kingae had siblings with positive oropharyngeal carriage.

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.

Recent lessons for the management of bone and joint infections

The epidemiology and clinical manifestations of osteoarticular infections are changing primarily as a result of the emergence of community-acquired methicillin-resistant Staphylococcus aureus infections. Multifocal disease, venous thrombosis and pathologic fractures are manifestations of CA-MRSA osteomyelitis. MRI is the diagnostic imaging modality of choice for musculoskeletal infections. Nafcillin/oxacillin or cefazolin remains the antibiotic of choice for treating infections caused by MSSA. A β-lactam antibiotic is recommended for Kingella kingae. Vancomycin and clindamycin are the first line agents for treating osteomyelitis caused by CA-MRSA. A short course of parenteral antibiotics followed by appropriate oral antibiotics is equivalent to total course of parenteral antibiotics for most patients and avoids the risks associated with PICCs. Surgical drainage of subperiosteal abscesses and surrounding pyomyositis is common with S. aureus clones currently circulating. Collaboration with hematologists for managing patients with venous thromboses is recommended.

Geme JW. Characterization of the Kingella kingae polysaccharide capsule and exopolysaccharide

Recent evidence indicates that Kingella kingae produces a polysaccharide capsule. In an effort to determine the composition and structure of this polysaccharide capsule, in the current study we purified capsular material from the surface of K. kingae strain 269-492 variant KK01 using acidic conditions to release the capsule and a series of steps to remove DNA, RNA, and protein. Analysis of the resulting material by gas chromatography and mass spectrometry revealed N-acetyl galactosamine (GalNAc), 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo), and galactose (Gal). Further analysis by NMR demonstrated two distinct polysaccharides, one consisting of GalNAc and Kdo with the structure →3)-β-GalpNAc-(1→5)-β-Kdop-(2→ and the other containing galactose alone with the structure →5)-β-Galf-(1→. Disruption of the ctrA gene required for surface localization of the K. kingae polysaccharide capsule resulted in elimination of GalNAc and Kdo but had no effect on the presence of Gal in bacterial surface extracts. In contrast, deletion of the pamABCDE locus involved in production of a reported galactan exopolysaccharide eliminated Gal but had no effect on the presence of GalNAc and Kdo in surface extracts. Disruption of ctrA and deletion of pamABCDE resulted in a loss of all carbohydrates in surface extracts. These results establish that K. kingae strain KK01 produces a polysaccharide capsule with the structure →3)-β-GalpNAc-(1→5)-β-Kdop-(2→ and a separate exopolysaccharide with the structure →5)-β-Galf-(1→. The polysaccharide capsule and the exopolysaccharide require distinct genetic loci for surface localization.

Characterization of TEM-1 β-Lactamase-Producing Kingella kingae Clinical Isolates

Kingella kingae is a human pathogen that causes pediatric osteoarticular infections and infective endocarditis in children and adults. The bacterium is usually susceptible to β-lactam antibiotics, although β-lactam resistance has been reported in rare isolates. This study was conducted to identify β-lactam-resistant strains and to characterize the resistance mechanism. Screening of a set of 90 K. kingae clinical isolates obtained from different geographic locations revealed high-level resistance to penicillins among 25% of the strains isolated from Minnesota and Iceland. These strains produced TEM-1 β-lactamase and were shown to contain additional ≥50-kb plasmids. Ion Torrent sequencing of extrachromosomal DNA from a β-lactamase-producing strain confirmed the plasmid location of the bla_TEM gene. An identical plasmid pattern was demonstrated by multiplex PCR in all β-lactamase producers. The porin gene's fragments were analyzed to investigate the relatedness of bacterial strains. Phylogenetic analysis revealed 27 single-nucleotide polymorphisms (SNPs) in the por gene fragment, resulting in two major clusters with 11 allele types forming bacterial-strain subclusters. β-Lactamase producers were grouped together based on por genotyping. Our results suggest that the β-lactamase-producing strains likely originate from a single plasmid-bearing K. kingae isolate that traveled from Europe to the United States, or vice versa. This study highlights the prevalence of penicillin resistance among K. kingae strains in some regions and emphasizes the importance of surveillance for antibiotic resistance of the pathogen.

Two atypical cases of Kingella kingae invasive infection with concomitant human rhinovirus infection

We describe two atypical cases of Kingella kingae infection in children diagnosed by PCR, one case involving a soft tissue abscess and one case a femoral Brodie abscess. Both patients had concomitant human rhinovirus infection. K. kingae strains, isolated from an oropharyngeal swab, were characterized by multilocus sequence typing and rtxA sequencing.

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.