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

摘要

For the past 5 decades, since the original characterization of Kingella kingae in the 1960s (1, 2), four additional species have been included in the Kingella genus, namely, K. denitrificans (3), K. oralis (4), K. potus (5), and (most recently) K. negevensis (6). Kingella organisms are asymptomatically harbored in the oropharynx in humans and animals, and all members of the genus Kingella but K. negevensis have been incriminated so far in invasive infections affecting, peculiarly, the musculoskeletal system, and occasionally the cardiac and central nervous systems, in humans (3–7). Kingella bacteria belong to the large Neisseriaceae family and are notoriously fastidious, and their recovery in routine culture media is suboptimal, which initially made their recognition as human pathogens difficult (7). In the early 1990s, the serendipitous discovery that inoculation of skeletal system exudates into blood culture vials improved the isolation of K. kingae revealed that this organism was a common etiology of joint and bone infections in young children (8). Subsequently, the advent of molecular diagnostic tools further improved the detection of K. kingae and established the species as the leading cause of skeletal system infections in children aged 6 to 48 months in countries where these modern detection methods are routinely employed (9–15). Initially, PCR assays targeting the small-subunit 16S rRNA gene followed by sequencing of the resulting amplicons enabled improvement of the detection of the organism from osteoarticular samples (9, 10). Thereafter, the development of a K. kingae-specific real-time quantitative PCR (qPCR) assay targeting the groEL gene (also known as cpn60, hsp60, or mopA), a housekeeping gene encoding a chaperone protein recognized as a universal bacterial marker (16, 17), allowed a further increase in the diagnostic capability for pediatric K. kingae arthritis compared to that of traditional PCR or culture methods (11–15). Subsequently, numerous in-house qPCR assays were optimized in an attempt to achieve maximum levels of specificity, sensitivity, and rapid detection of K. kingae for a wide array of clinical specimens, including joint fluids, bone (12–15), oropharyngeal specimens (18, 19), and occasionally blood samples (19–21), cerebrospinal fluid (22), or cardiac tissues (20).