Kingella kingae PilC1 and PilC2 are adhesive multifunctional proteins that promote bacterial adherence, twitching motility, DNA transformation, and pilus biogenesis.

The gram-negative bacterium Kingella kingae is a leading cause of osteoarticular infections in young children and initiates infection by colonizing the oropharynx. Adherence to respiratory epithelial cells represents an initial step in the process of K. kingae colonization and is mediated in part by type IV pili. In previous work, we observed that elimination of the K. kingae PilC1 and PilC2 pilus-associated proteins resulted in non-piliated organisms that were non-adherent, suggesting that PilC1 and PilC2 have a role in pilus biogenesis. To further define the functions of PilC1 and PilC2, in this study we eliminated the PilT retraction ATPase in the ΔpilC1ΔpilC2 mutant, thereby blocking pilus retraction and restoring piliation. The resulting strain was non-adherent in assays with cultured epithelial cells, supporting the possibility that PilC1 and PilC2 have adhesive activity. Consistent with this conclusion, purified PilC1 and PilC2 were capable of saturable binding to epithelial cells. Additional analysis revealed that PilC1 but not PilC2 also mediated adherence to selected extracellular matrix proteins, underscoring the differential binding specificity of these adhesins. Examination of deletion constructs and purified PilC1 and PilC2 fragments localized adhesive activity to the N-terminal region of both PilC1 and PilC2. The deletion constructs also localized the twitching motility property to the N-terminal region of these proteins. In contrast, the deletion constructs established that the pilus biogenesis function of PilC1 and PilC2 resides in the C-terminal region of these proteins. Taken together, these results provide definitive evidence that PilC1 and PilC2 are adhesins and localize adhesive activity and twitching motility to the N-terminal domain and biogenesis to the C-terminal domain.

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.

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.

A multicentre evaluation and expert recommendations of use of the newly developed BioFire Joint Infection polymerase chain reaction panel.

Septic arthritis is a serious condition with significant morbidity and mortality, routinely diagnosed using culture. The FDA has recently approved the rapid molecular BioFire® Joint Infection Panel (BJIP) for synovial fluid. We aimed to evaluate the BJIP compared to culture and its potential use in patient management. A multicentre retrospective evaluation of BJIP was conducted in the UK and Ireland. Positive percent agreement (PPA) and negative percent agreement (NPA) were calculated between the BJIP and routine culture. A multidisciplinary team (MDT) discussion addressing the optimal or potential case use of the assay practice was facilitated. Three hundred ninety-nine surplus synovial fluid samples (~ 70% from native joints) from eight centres were processed using BJIP in addition to routine culture. An increased yield of positive results was detected using BJIP compared to routine culture (98 vs 83), giving an overall PPA of 91.6% and overall NPA of 93% for the BJIP compared to culture results. The BJIP detected resistant markers and additional organisms that could influence antibiotic choices including Neisseria gonorrhoeae and Kingella kingae. The MDT agreed that the assay could be used, in addition to standard methods, in adult and children patients with specialist advice use based on local needs. Rapid results from BJIP were assessed as having potential clinical impact on patient management. Organisms not included in the panel may be clinically significant and may limit the value of this test for PJI.

Native joint infections in Iceland 2003-2017: an increase in postarthroscopic infections.

OBJECTIVES: Nationwide study on the epidemiology, clinical characteristics and outcomes among patients with native joint infection (NJI) in Iceland, 2003-2017. METHODS: All positive synovial fluid culture results in Iceland were identified and medical records reviewed. RESULTS: A total of 299 NJI (40 children and 259 adults) were diagnosed in Iceland in 2003-2017, with a stable incidence of 6.3 cases/100 000/year, but marked gender difference among adults (33% women vs 67% men, p<0.001). The knee joint was most commonly affected, and Staphylococcus aureus was the most common isolate in both adults and children, followed by various streptococcal species in adults and Kingella kingae in children. NJI was iatrogenic in 34% of adults (88/259) but comprised 45% among 18-65 years and a stable incidence. Incidence of infections following arthroscopic procedures in adults increased significantly compared with the previous decade (9/100 000/year in 1990-2002 vs 25/100 000/year in 2003-2017, p<0.01) with no significant increase seen in risk per procedure. The proportion of postarthroscopic NJI was 0.17% overall but 0.24% for knee arthroscopy. Patients with postarthroscopic infection were more likely to undergo subsequent arthroplasty when compared with other patients with NJI (p=0.008). CONCLUSIONS: The incidence of NJI in Iceland has remained stable. The proportion of iatrogenic infections is high, especially among young adults, with an increase seen in postarthroscopic infections when compared with the previous decade. Although rare, NJI following arthroscopy can be a devastating complication, with significant morbidity and these results, therefore, emphasise the need for firm indications when arthroscopic treatment is considered.

Simplified antibiotic treatment for paediatric osteoarticular infections achieved good outcomes.

AIM: Early diagnosis of osteoarticular infections (OAI) in children and effective treatment prevents complications. The objective of this study was to evaluate effectiveness and safety of shortened intravenous antibiotic treatment of OAI. Incidence, diagnostics and pathogens of paediatric OAI were assessed. METHODS: This retrospective study included all paediatric OAI admissions to The Children's Hospital Iceland in 2006-2020. The treatment was evaluated by dividing the study cohort into two groups. The simplified treatment group received intravenous antibiotics for less than 7 days. The longer intravenous group received intravenous antibiotics for a minimum of 7 days. RESULTS: In total, 205 cases of OAI were included: 106 osteomyelitis, 83 septic arthritis and 16 with both. Age standardised incidence was 17 per 100,000 children and decreased over the study period (p = 0.004). A pathogen was identified in 37% (75/205) of cases of which 65% (49/75) were Staphylococcus aureus and 12% (9/75) Kingella kingae. Simplified treatment was not associated with increased risk of complications. CONCLUSION: This study supports claims that simplified treatment for OAI is safe and effective. Further simplification of treatment might be viable. For uncertain reasons the incidence of OAI was decreasing in Iceland, predominantly in young children.

Microbiology of septic arthritis in young Auckland children.

BACKGROUND: Kingella kingae is an important cause of septic arthritis in young children, with modern laboratory methods leading to increased detection. Prevalence of this pathogen in New Zealand, where there are high rates of childhood infections due to Staphylococcus aureus and Streptococcus pyogenes, is not known. METHODS: We conducted a retrospective review of children <5 years with septic arthritis (without osteomyelitis) at a tertiary children's hospital in Auckland, over 10 years (2005-2014). Data were collected on demographics, microbiology, clinical presentation, investigations and management. RESULTS: Of the 68 cases of septic arthritis, 57 (83.8%) occurred in children aged <24 months. Among those <3 months, Streptococcus agalactiae (Group B streptococcus) was predominant (45.5% of 11 cases), followed by S. aureus (36.4%). The most common pathogen in those 3 to <12 months was Streptococcus pneumoniae (38.5% of 13 cases). In children aged 12 to <24 months, K. kingae was most common (30.3% of 33 cases). Of the 12 cases of K. kingae, 91.7% were identified from synovial fluid culture. All K. kingae isolates were susceptible to amoxicillin. CONCLUSIONS: K. kingae is the leading pathogen in septic arthritis in New Zealand children aged 12 to <24 months. Routine inoculation of synovial fluid into blood culture bottles at time of sample collection, in addition to use of polymerase chain reaction methods, should be encouraged to improve detection rates. For infants and preschool children presenting with single joint septic arthritis, empiric antibiotics should include cover for S. aureus and K. kingae.

Characteristics of Children With Culture Negative Acute Hematogenous Musculoskeletal Infections.

BACKGROUND: Identifying the causative pathogen for acute hematogenous musculoskeletal infections (MSKIs) allows for directed antimicrobial therapy and diagnostic confidence. However, 20% to 50% of children with acute MSKIs remain culture negative. The objective of this study was to compare characteristics of culture negative MSKI patients to those where a pathogen is identified. METHODS: Electronic medical records of children admitted between July 2014 to September 2018 to a single quaternary care pediatric hospital with acute MSKIs were retrospectively reviewed. Clinical and demographic characteristics were compared between culture positive and culture negative MSKIs. RESULTS: A total of 170 patients were included of whom 43 (25%) were culture negative. All culture negative patients had at least 1 culture type obtained, and the majority (84%) had both blood and source cultures performed. When compared with patients with a causative pathogen identified, culture negative patients were younger (2.3 vs. 9.8 y), smaller (13.5 vs. 31.6 kg), less likely to be febrile on arrival (56% vs. 77%), less likely to have an abscess on imaging (23% vs. 48%), and were more likely to have uncomplicated septic arthritis (35% vs. 8%). No critically ill patient was culture negative. Seven culture negative patients had additional Kingella kingae testing performed, none of which were positive. CONCLUSIONS: Despite targeted and standardized efforts to identify causative bacteria, 25% of children with acute MSKIs never have a pathogen identified. Culture negative patients are younger, less febrile, are less likely to have an abscess, and more likely to have isolated septic arthritis. LEVEL OF EVIDENCE: This is a retrospective cohort study interested in identifying patient characteristics that predict rate of culture positivity for acute MSKIs. This study meets criteria for Level II evidence.

First report of Kingella kingae diagnosed in pediatric bone and joint infections in Morocco.

BACKGROUND: The progress of diagnostic strategies and molecular methods improved the detection of Kingella kingae in bone and joint infections, and now, Kingella kingae is being increasingly recognized as the most frequent cause of bone and joint infection BJI in early childhood. The main objective of this prospective study is to report the frequency of Kingella Kingae in negative culture bone and joint pediatric infections, and to describe the clinical and biologic features of these children. METHODS: From December 2016 to June 2019, we selected all hospitalized patients with suspected BJI. When culture was negative on the fifth day, children under 10 years were subsequently included in the study, and PCR assay was performed systematically for researching K. kingae specific gene cpn60. Microbial culture and identification were made using standard bacteriological methods. The demographics, clinical, laboratory, radiographic and clinical features were reviewed from medical records. RESULTS: We enrolled 65 children with culture negative BJI, 46 of them having under 10 years old have been screened for the cpn60 gene. Thus, the gene encoding Kingella kingae was positive for 27 BJI cases (58.7%). The mean age of children was 3.02 years, 55.6% were aged 6 months-4 years and 29.6% of them were aged 5-10 years. The male to female ratio was 1.7 and 16 cases (59.26%) occurred during the fall-winter period. The most frequent BJI type was septic arthritis (77.8%) and the most affected sites were knee (51.9%) and hip (37.0%). We recorded a mild clinical picture with normal to mildly raised inflammatory markers. All patients had good clinical and functional outcomes, with no serious orthopedic sequelae.. CONCLUSION: K kingae is an important pathogen of culture-negative BJI in Moroccan children. PCR testing should be performed in culture-negative cases of children not only in the typical age range of 6 months to 4 years. When implemented in the routine clinical microbiology laboratory, a specific K. kingae PCR assay can provide a better diagnostic performance of BJI.

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.

Changing aetiology of paediatric septic arthritis.

The management of septic arthritis in children requires the prompt administration of antibiotic therapy and the identification of the causative pathogen. In the past, Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae and Haemophilus influenzae type b were considered the main causative agents of the disease, but a substantial fraction of presumptive joint infections remained unconfirmed by conventional bacteriologic cultures. In the last two decades, our knowledge of the aetiology of paediatric infectious arthritis has substantially changed as the result of the implementation of vaccination programmes against H. influenzae type b and pneumococci, and by the use of improved detection methods. In 1988, the inoculation of synovial fluid aspirates into blood culture vials revealed that Kingella kingae, a commensal member of the oropharyngeal microbiota, was the prime aetiology of skeletal system infections in children aged 6-48 months. The clinical presentation of K. kingae arthritis is subtle, and the disease is frequently missed by classic clinical and laboratory diagnostic criteria. Many children are afebrile, the acute phase reactants levels and the white blood cell counts in the blood and synovial fluid specimens are frequently normal, requiring a high clinical acumen. Increasing use of sensitive molecular methods in recent years, and particularly nucleic acid amplification tests that target K. kingae-specific genes, has further improved the detection of this elusive pathogen, demonstrated that it is responsible for 30-93% of all cases of septic arthritis below 4 years of age and reduced the fraction of culture-negative infections.

Clinical presentations of Kingella kingae musculoskeletal infections in South Australian children.

AIM: This study aimed to alert clinicians to the spectrum of presentations of Kingella kingae musculoskeletal infections. METHODS: Between August 2010 and March 2018, 55 children presented with positive K. kingae polymerase chain reaction on joint fluid, bone or deep soft tissue collections involving the limbs and subsequently underwent retrospective medical record, radiological and laboratory review. Demographics and clinical information are presented. RESULTS: Median age at presentation was 15.9 months (range 4.3 months-10.7 years) and 64% were male. Septic arthritis was the most common diagnosis (95%), median duration of symptoms was 4 days, 65% had a preceding infection (e.g. upper respiratory or gastrointestinal) and 22% re-presented to emergency departments after prior discharge. The lower limb was involved in 84%, with the knee being most affected (55%). If the lower limb was involved, 82% of previously weight-bearing children had a limp or were unable to weight bear. On presentation, median temperature was 36.7°C and inflammatory markers were mildly elevated. No blood cultures grew K. kingae. Five synovial fluid cultures were positive for K. kingae. Plain radiography showed effusion, soft tissue swelling or a lesion in 53% of patients. All 41 ultrasounds showed effusion, soft tissue swelling or synovial thickening. One patient with delayed diagnosis later presented with avascular necrosis of the femoral head. CONCLUSION: Kingella kingae is difficult to diagnose due to non-specific symptoms, absence of fevers and often unremarkable blood tests. Despite generally having good long-term outcomes, our case of avascular necrosis suggests accurate diagnosis and treatment are important.

Primary Septic Arthritis Among Children 6 to 48 Months of Age: Implications for PCR Acquisition and Empiric Antimicrobial Selection.

INTRODUCTION: Primary septic arthritis requires unique evaluation and treatment considerations for children in the 6- to 48-month age range because of the spectrum of identified pathogens and high rate of negative cultures. The purpose of this study is to evaluate primary septic arthritis in this age group in order to differentiate children with infection caused by Kingella kingae from those with other confirmed pathogens and those with no identified pathogen. METHODS: Preschool children who underwent multidisciplinary evaluation and treatment for septic arthritis between 2009 and 2019 were retrospectively studied. Three cohorts were established for comparison of clinical and laboratory features of primary septic arthritis: (1) confirmed K. kingae, (2) confirmed other pathogen, and (3) presumed (without identified pathogen). RESULTS: Among 139 children with septic arthritis, 40 (29%) were confirmed K. kingae, 29 (21%) other pathogen, and 70 (50%) presumed. Children with Kingella and those with presumed septic arthritis had significantly lower initial C-reactive protein (4.8 and 4.5 vs. 9.3 mg/dL) and fewer febrile hospital days (0.2 and 0.4 vs. 1.3 d) than children with other confirmed pathogens. Children with other pathogens had higher rates of bacteremia (38% vs. 0%) and positive joint fluid cultures (86% vs. 15%) than that of children with Kingella. The rate of polymerase chain reaction (PCR) acquisition was 38 of 40 (95.0%) Kingella cases, 18 of 29 (62.1%) other pathogen cases, and 33 of 70 (47.1%) presumed cases. CONCLUSIONS: K. kingae was the most commonly identified pathogen among 6-month to 4-year-old children. The Kingella and other identified pathogens in this study serve to guide empiric antimicrobial recommendations for this age range. Because of similarities between children with septic arthritis because of K. kingae and those with no identified pathogen, it is likely that an unrecognized burden of Kingella resides in culture negative cases, particularly if no PCR is sent. Systematic evaluation, including PCR acquisition, and a high index of suspicion for K. kingae are recommended to thoroughly evaluate septic arthritis in preschool children. LEVEL OF EVIDENCE: Level III-Retrospective cohort comparison.

Endovascular Infection with Kingella kingae Complicated by Septic Arthritis in Immunocompromised Adult Patient.

We report a case of Kingella kingae endovascular infection in an immunocompromised elderly patient in Israel who had culture-negative septic arthritis. This case highlights potential sources of metastatic infection other than infective endocarditis, and emphasizes the need for molecular diagnostic methods in detection of pathogens in culture-negative septic arthritis in immunocompromised patients.

Binding of Kingella kingae RtxA Toxin Depends on Cell Surface Oligosaccharides, but Not on ß2 Integrins.

The Gram-negative coccobacillus Kingella kingae is increasingly recognized as an important invasive pediatric pathogen that causes mostly bacteremia and skeletal system infections. K. kingae secretes an RtxA toxin that belongs to a broad family of the RTX (Repeats in ToXin) cytotoxins produced by bacterial pathogens. Recently, we demonstrated that membrane cholesterol facilitates interaction of RtxA with target cells, but other cell surface structures potentially involved in toxin binding to cells remain unknown. We show that deglycosylation of cell surface structures by glycosidase treatment, or inhibition of protein N- and O-glycosylation by chemical inhibitors substantially reduces RtxA binding to target cells. Consequently, the deglycosylated cells were more resistant to cytotoxic activity of RtxA. Moreover, experiments on cells expressing or lacking cell surface integrins of the ß2 family revealed that, unlike some other cytotoxins of the RTX family, K. kingae RtxA does not bind target cells via the ß2 integrins. Our results, hence, show that RtxA binds cell surface oligosaccharides present on all mammalian cells but not the leukocyte-restricted ß2 integrins. This explains the previously observed interaction of the toxin with a broad range of cell types of various mammalian species and reveals that RtxA belongs to the group of broadly cytolytic RTX hemolysins.

Synthesis of the ß-linked GalNAc-Kdo disaccharide antigen of the capsular polysaccharide of Kingella kingae KK01.

The first construction of the challenging ß-(1 → 5)-linked GalNAc-Kdo skeleton is described for the synthesis of the disaccharide antigen of the capsular polysaccharide of Kingella kingae KK01. TfOH-catalyzed glycosylation of N-Troc-protected d-galactosaminyl N-phenyl trifluoroacetimidate with a sterically hindered 5-hydroxyl group of the ß-Kdo building block in toluene proceeded smoothly to provide the desired disaccharide in excellent yield with satisfactory ß-selectivity. An optimal sequence for the deprotection of the disaccharide skeleton was found to access the disaccharide antigen of Kingella kingae KK01 for further immunological studies.

Inflammatory markers limitations in the diagnosis of pediatric calcaneal osteomyelitis.

Calcaneal osteomyelitis is an uncommon, but clinically important emergent condition in the differential of the limping child. Early recognition is paramount to prevent complications from delayed diagnosis like formation of periosteal abscesses or growth plate injury. The diagnosis of pediatric osteoarticular infection relies on a combination of clinical exam, imaging and inflammatory markers. Erythrocyte sedation rate (ESR) and C-reactive protein (CRP) have reported sensitivities for osteomyelitis of 94% and 95%, respectively. However, clinicians should be aware that certain clinical factors can decrease the reliability of inflammatory markers in this pediatric condition. Location of infection in small bones like the calcaneus can lead to significantly lower sensitivities than in long bones. Pretreatment with antibiotics prior presentation can also decrease the reliability of ESR and CRP. In this case, we highlight two unique clinical factors that diminish the sensitivity of commonly used inflammatory markers in the diagnosis of pediatric osteomyelitis.

[Kingella kingae bone and joint infections]. / Arthrites à Kingella kingae chez l'enfant : à propos de six cas.

We report six cases of children with probable or confirmed Kingella kingae bone and joint infections (BJI) and discuss the role of this pathogen in the pediatric population. The advent of Polymerase Chain Reaction (PCR) led to the recognition of the importance of Kingella kingae in several human diseases, particularly in BJI affecting children aged 6 to 48 months. Kingella kingae infections in children have most often a good prognosis provided that the diagnosis is discussed, appropriate diagnostic methods are performed and effective antibiotics are prescribed.

Nous rapportons 6 cas probables ou confirmés d'infections ostéoarticulaires (IOA) à Kingella kingae et proposons une revue de l'implication de ce pathogène en pédiatrie. L'avènement de la PCR (Polymerase Chain Reaction) a mis en lumière son rôle dans diverses maladies humaines, en particulier les IOA chez les enfants âgés de 6 à 48 mois. Le pronostic des infections à Kingella kingae chez l'enfant est le plus souvent bon, pour autant que le diagnostic soit évoqué, que les méthodes diagnostiques adéquates soient utilisées et qu'une antibiothérapie appropriée soit instaurée.

Kingella kingae Surface Polysaccharides Promote Resistance to Human Serum and Virulence in a Juvenile Rat Model.

Kingella kingae is a Gram-negative coccobacillus that is increasingly being recognized as an important cause of invasive disease in young children. The pathogenesis of K. kingae disease begins with colonization of the oropharynx, followed by invasion of the bloodstream, survival in the intravascular space, and dissemination to distant sites. Recent studies have revealed that K. kingae produces a number of surface factors that may contribute to the pathogenic process, including a polysaccharide capsule and an exopolysaccharide. In this study, we observed that K. kingae was highly resistant to the bactericidal effects of human serum complement. Using mutant strains deficient in expression of capsule, exopolysaccharide, or both in assays with human serum, we found that elimination of both capsule and exopolysaccharide was required for efficient binding of IgG, IgM, C4b, and C3b to the bacterial surface and for complement-mediated killing. Abrogation of the classical complement pathway using EGTA-treated human serum restored survival to wild-type levels by the mutant lacking both capsule and exopolysaccharide, demonstrating that capsule and exopolysaccharide promote resistance to the classical complement pathway. Consistent with these results, loss of both capsule and exopolysaccharide eliminated invasive disease in juvenile rats with an intact complement system but not in rats lacking complement. Based on these observations, we conclude that the capsule and the exopolysaccharide have important redundant roles in promoting survival of K. kingae in human serum. Each of these surface factors is sufficient by itself to fully prevent serum opsonin deposition and complement-mediated killing of K. kingae, ultimately facilitating intravascular survival and promoting K. kingae invasive disease.

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.