Molecular Tests That Target the RTX Locus Do Not Distinguish between Kingella kingae and the Recently Described Kingella negevensis Species.

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 infections. However, the present study shows that , a species newly identified in young children, harbors an identical RTX locus, raising the question of whether can be misidentified as by clinical microbiology laboratories. comparison of sp. RTX and genes and studies provided evidence that targeting the and genes could not differentiate between strains of and , whereas targeting the gene could. This prompted the design of a highly specific and sensitive qPCR assay targeting (). 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 -specific , -specific (), and qPCR assays. Forty-two specimens were positive, including 41 that were also positive and 1 (the remaining one) that was positive. Thus, this study discloses an invasive infection caused by in humans and demonstrates that targeting the RTX locus cannot be used for the formal diagnosis of infections. These findings stress the need for further studies on the epidemiology of asymptomatic carriage and invasive infections caused by in humans.