Characterization of Integrative and Conjugative Element ICE Kp1 -Associated Genomic Heterogeneity in a Klebsiella pneumoniae Strain Isolated from a Primary Liver Abscess

Genomic heterogeneity has been shown to be associated with Klebsiella pneumoniae strains causing pyogenic liver abscesses (PLA) and metastatic infections. In order to explore the mechanism responsible for genomic heterogeneity in K. pneumoniae , we compared the complete genomic sequences of strains NTUH-K2044 and MGH78578. An ∼76-kbp DNA fragment located adjacent to an asparagine ( asn ) tRNA gene was present in NTUH-K2044 but not in MGH78578. This fragment could be divided into three regions with different functions, and structurally it resembled a functional integrative and conjugative element (ICE), ICE Ec1 , in Escherichia coli . The 5′ region of this fragment contained genes similar to a high-pathogenicity island (HPI) of Yersinia pestis and Yersinia pseudotuberculosis . The middle region was similar to part of a large plasmid in K. pneumoniae , and the 3′ region contained genes responsible for DNA conjugative transfer. Therefore, this DNA fragment was designated ICE Kp1 . Precise excision and extrachromosomal circularization of ICE Kp1 were detected in K. pneumoniae wild-type strain NTUH-K2044. ICE Kp1 could integrate into the asn tRNA loci of the chromosome of another K. pneumoniae isolate. The prevalence of ICE Kp1 was higher in PLA strains (38 of 42 strains) than in non-tissue-invasive strains (5 of 32 strains). Therefore, ICE Kp1 may contribute to the transmission of the HPI and result in K. pneumoniae PLA infection-associated genomic heterogeneity.