Search

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., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

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., (© 2014 The Authors Clinical Microbiology and Infection © 2014 European Society of Clinical Microbiology and Infectious Diseases.)

Kingella kingae is an emerging pathogen causing osteoarticular infections in pediatric patients. Electron microscopy of K. kingae clinical isolates revealed the heterogeneously-sized membranous structures blebbing from the outer membrane that were classified as outer membrane vesicles (OMVs). OMVs purified from the secreted fraction of a septic arthritis K. kingae isolate were characterized. Among several major proteins, K. kingae OMVs contained virulence factors RtxA toxin and PilC2 pilus adhesin. RtxA was also found secreted as a soluble protein in the extracellular environment indicating that the bacterium may utilize different mechanisms for the toxin delivery. OMVs were shown to be hemolytic and possess some leukotoxic activity while high leukotoxicity was detected in the non-hemolytic OMV-free component of the secreted fraction. OMVs were internalized by human osteoblasts and synovial cells. Upon interaction with OMVs, the cells produced increased levels of human granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 6 (IL-6) suggesting that these cytokines might be involved in the signaling response of infected joint and bone tissues during natural K. kingae infection. This study is the first report of OMV production by K. kingae and demonstrates that OMVs are a complex virulence factor of the organism causing cytolytic and inflammatory effects on host cells., (Copyright © 2011 Elsevier Ltd. All rights reserved.)