WGS-based characterization of putative hypervirulent Klebsiella pneumoniae identified in a tertiary care hospital in Germany

Introduction: Hypervirulent Klebsiella pneumoniae strains (hvKp), in contrast to classical K. pneumoniae strains, can cause invasive community-acquired infections in healthy patients of all ages. In this study, K. pneumoniae isolates from routine microbiological diagnostics were tested via string-test for hypermucoviscous phenotype and PCR for virulence genes to screen for hvKp, which were further analyzed by whole-genome sequencing (WGS).Goals: The prevalence of "hidden" hypervirulent hvKp, including non-invasive strains and their population structure should be analyzed in a tertiary-care hospital in Southern Germany.Materials/methods: For the study period 1.5 years, all K. pneumoniae isolates were string-tested. A multiplex PCR for hvKp genes was applied to all string-test positive isolates. PCR-positive isolates were subjected to WGS to determine genotyping and phylogeny.Results: A total of 10.9% (331/3044) isolates with hmKp phenotype were detected by string-test. The patients" age rangend from 0 to 95 years, with a mean of 69 years. In total, 13.3% (44/331) isolates were tested positive by PCR for genes associated with hvKp. cgMLST revealed that 41.5% of sequenced isolates belonged to international hvKp clonal lineages ST23/K1 with high virulence scores and close phylogenetic relationships. In contrast, 22.6% of isolates belonged to the ST86/K2 with lower virulence scores. Isolates of liver abscesses (7.5%) belonged to ST23, ST25 and ST268, but without phylogenetic relatedness to other isolates.Summary: We identified hypervirulent K. pneumoniae within the study period with an overall prevalence of 1.4%. No transmissions were identified. Isolates were assigned to the international hvKp lineage ST23/K1 and lineage ST86, bearing the potential to spread further in the community. The known association of multidrug-resistance ST86, was not observed in this study. Presented cases of liver abscesses seem to represent individual occurrences, so far. In conclusion, the screening of hmKp phenotypes in routine diagnostics seems to be a suitable surveillance method. Further, the population size and structure of "hidden" putative hvKp were more complex than expected.