An Assessment of Siderophore Production, Mucoviscosity, and Mouse Infection Models for Defining the Virulence Spectrum of Hypervirulent Klebsiella pneumoniae.

Thomas A Russo,Ellie Camanzo,Ulrike Macdonald,Sidra Hassan,Brendan Corey,Francois Lebreton,Patrick Mcgann,Vincent B Young

doi:10.1128/msphere.00045-21

Thomas A Russo, Ellie Camanzo + Show 6 more

Open Access

https://doi.org/10.1128/msphere.00045-21

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Abstract

ABSTRACTHypervirulent Klebsiella pneumoniae (hvKp) bacteria are more virulent than classical K. pneumoniae (cKp) with resultant differences in clinical manifestations and management. It is unclear whether all hvKp isolates share a similar pathogenic potential. This report assessed the utility of siderophore production, mucoviscosity, and murine infection for defining the virulence spectrum of hvKp. Three strain cohorts were identified and defined based on the CD1 mouse subcutaneous (SQ) challenge model: (i) fully virulent hvKp strains (fvhvKp), lethal at a challenge inoculum (CI) of ≤103 CFU; (ii) partially virulent hvKp strains (pvhvKp), lethal at a CI of >103 to 107 CFU; (iii) classical K. pneumoniae, not lethal at a CI of 107 CFU. Quantitative siderophore and mucoviscosity assays differentiated fvhvKp and pvhvKp strains from cKp strains but were unable to differentiate between the fvhvKP and pvhvKP strain cohorts. However, SQ challenge of CD1 mice and intraperitoneal (IP) challenge of CD1 and BALB/c mice, but not C57BL/6 mice, were able to discriminate between an fvhvKp and a pvhvKp strain; SQ challenge of CD1 mice may have the greatest sensitivity. cKp was differentiated from hvKp both by SQ challenge of CD1 mice and IP challenge of all three mouse strains. These data identify a means to define the relative virulence of hvKP strains. It remains unclear whether the observed differences of hvKp virulence in mice translates to human infection. However, these data can be used to sort random collections of K. pneumoniae strains into fvhvKp and pvhvKp strain cohorts and assess for differences in clinical manifestations and outcomes.IMPORTANCE The pathogenic potential of hvKp strains is primarily mediated by a large virulence plasmid. The minimal set of genes required for the full expression of the hypervirulent phenotype is undefined. A number of reports describe hvKp strains possessing only a portion of the virulence plasmid; the clinical consequences of this are unclear. Therefore, the goal of this report was to determine whether virulence among hvKp strains varied and, if so, how to best identify the relative virulence of hvKp isolates. Data demonstrate hvKp pathogenic potential varies in CD1 and BALB/c murine infection models. In contrast, measurements of siderophore production and mucoviscosity were unable to discriminate the differences in hvKp isolate virulence observed in mice. This information can be used in future studies to determine the mechanisms responsible for differences between fully virulent hvKp and partially virulent hvKp and whether the differences observed in mice translate to disease in humans.

Highlights

Hypervirulent Klebsiella pneumoniae bacteria are more virulent than classical K. pneumoniae with resultant differences in clinical manifestations and management
This result was validated in the outbred CD1 murine infection model, which was highly discriminatory for differentiating Hypervirulent Klebsiella pneumoniae (hvKp)-rich and classical K. pneumoniae (cKp)-rich strain cohorts that were developed based on clinical criteria from human infection [8]
The following three K. pneumoniae strain cohorts were defined by their phenotype after SQ challenge of outbred CD1 mice; fully virulent hvKp strains were lethal at a challenge inoculum (CI) of #103 CFU; partially virulent hvKp strains were lethal at a CI .103 to 107 CFU; and classical K. pneumoniae were not lethal at a CI of 107 CFU

Summary

Introduction

Hypervirulent Klebsiella pneumoniae (hvKp) bacteria are more virulent than classical K. pneumoniae (cKp) with resultant differences in clinical manifestations and management. The possession of the combination of the iucA, iroB, peg-344, prmpA, and prmpA2 genes which reside on the canonical hvKp virulence plasmid, albeit imperfectly, most accurately predicts whether a strain possesses the hypervirulent phenotype This result was validated in the outbred CD1 murine infection model, which was highly discriminatory for differentiating hvKp-rich and cKp-rich strain cohorts that were developed based on clinical criteria from human infection [8]. Hybrid plasmids that consist of antimicrobial resistance genes and a fraction of the hvKp-specific virulence plasmid have been described [14,15,16] It remains unclear which combination of genetic elements residing on the hvKp-specific virulence plasmid is needed for the full expression of the hypervirulent phenotype, the relative importance of individual elements, and whether these differences affect the pathogenic potential of a given hvKp strain. The accuracy of other mouse strains and challenge routes has been less rigorously assessed

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