Journal of Clinical Microbiology · 2017 · 29 citations · 35 references
<i>Kingella kingae</i> is an important invasive pathogen in early childhood. The organism elaborates an RTX toxin presumably restricted to this species. Consequently, real-time quantitative PCR (qPCR) assays targeting the RTX locus have been developed in recent years and are gaining increasing use for the molecular diagnosis of <i>K. kingae</i> infections. However, the present study shows that <i>Kingella negevensis</i>, a <i>Kingella</i> species newly identified in young children, harbors an identical <i>Kingella</i> RTX locus, raising the question of whether <i>K. negevensis</i> can be misidentified as <i>K. kingae</i> by clinical microbiology laboratories. <i>In silico</i> comparison of <i>Kingella</i> sp. RTX and <i>groEL</i> genes and <i>in vitro</i> studies provided evidence that targeting the <i>rtxA</i> and <i>rtxB</i> genes could not differentiate between strains of <i>K. kingae</i> and <i>K. negevensis</i>, whereas targeting the <i>groEL</i> gene could. This prompted the design of a highly specific and sensitive qPCR assay targeting <i>K. negevensis groEL</i> (<i>kngroEL</i>). Ninety-nine culture-negative osteoarticular specimens from 99 children younger than 4 years of age were tested with a conventional 16S rRNA gene-based broad-range PCR assay and <i>Kingella</i>-specific <i>rtxB</i>, <i>K. kingae</i>-specific <i>groEL</i> (<i>kkgroEL</i>), and <i>kngroEL</i> qPCR assays. Forty-two specimens were <i>rtxB</i> positive, including 41 that were also <i>kkgroEL</i> positive and 1 (the remaining one) that was <i>kngroEL</i> positive. Thus, this study discloses an invasive infection caused by <i>K. negevensis</i> in humans and demonstrates that targeting the RTX locus cannot be used for the formal diagnosis of <i>K. kingae</i> infections. These findings stress the need for further studies on the epidemiology of asymptomatic carriage and invasive infections caused by <i>K. negevensis</i> in humans.
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