KpSC-ID: a multiplex real-time PCR assay for the simultaneous detection of the Klebsiella pneumoniae species complex and specific identification of Klebsiella pneumoniae, Klebsiella quasipneumoniae and Klebsiella variicola

The Klebsiella pneumoniae species complex (KpSC) comprises five closely related bacterial species, namely Klebsiella pneumoniae, Klebsiella quasipneumoniae, Klebsiella variicola, Klebsiella quasivariicola and Klebsiella africana. The KpSC is ubiquitous in the environment and is also an important human pathogen, particularly associated with healthcare-associated infections. The accurate detection and differentiation of the KpSC is challenging owing to the close phenotypic and genotypic identity (93–95% average nucleotide identity) shared between these members. Current diagnostic assays either fail to detect and identify all KpSC members or misidentify some KpSC members as K. pneumoniae sensu stricto. It is currently estimated that ~20% of human infections are caused by members of the KpSC other than K. pneumoniae. This leads to underreporting of some KpSC members in both clinical and environmental settings, which impacts our understanding of the importance of each species. Furthermore, it limits our understanding of the global and local epidemiological impact of some members of the KpSC. In this study, a rapid multiplex real-time PCR assay (KpSC-ID) was designed and developed to detect all KpSC members while simultaneously identifying the predominant human pathogens K. pneumoniae, K. quasipneumoniae and K. variicola. Assay performance was verified in silico using a panel of over 1,000 publicly available genome sequences and experimentally validated using a panel of genomic DNA extracted from 54 Enterobacteriaceae. The assay displayed excellent specificity against over 1,000 genome sequences tested in silico. During in vitro validation, the pan-KpSC assay detected each (29/29) KpSC species and strains tested. For the species-specific assays, 100% specificity was demonstrated in the K. pneumoniae, K. quasipneumoniae and K. variicola assays, respectively. Sensitivity of 10 genomic equivalents was demonstrated for each assay. Ultimately, the diagnostic assay developed in this study can improve our understanding of the significance of KpSC members, which is important when investigating their routes of transmission and epidemiology.