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. 2021 Jun 22;13(1):40.
doi: 10.1186/s13099-021-00439-z.

Virulence among different types of hypervirulent Klebsiella pneumoniae with multi-locus sequence type (MLST)-11, Serotype K1 or K2 strains

Tsui-Chin Wang #  1 , Jung-Chung Lin #  2 , Jen-Chang Chang  1 , Ya-Wen Hiaso  2 , Ching-Hsun Wang  2 , Sheng-Kung Chiu  2 , Chang-Phone Fung  3 , Feng-Yee Chang  4 , L Kristopher Siu  5   6   7
Affiliations
Free PMC article

Virulence among different types of hypervirulent Klebsiella pneumoniae with multi-locus sequence type (MLST)-11, Serotype K1 or K2 strains

Tsui-Chin Wang et al. Gut Pathog. .
Free PMC article

Abstract

Background: Two different types of hypervirulent K. pneumoniae (HvKp), the MLST-11 and serotype K1/K2 strains, have been frequently described in recent studies. Although these two types of strains were described to be HvKp, their virulence was not compared. In this study, in vitro and in vivo approaches were used to assess differences in virulence.

Materials and methods: A total of twenty-nine isolates, including 6 strains of each of serotype K1 and K2 isolates and 17 strains of ST11 isolates, were selected for this study. Phenotypic tests of virulence were performed by the string test and analysis of the virulent associated genes was detected by PCR. In vitro models of serum resistance and phagocytosis were used as the parameters to assess the virulence. In-frame deletion of virulence-associated genes was performed to study their contributions to virulence. The median lethal dose, i.e., the LD50, in mice was determined following IP injection.

Results: Although serotype K1 and K2 strains and ST11 isolates had similar virulence gene profiles, the ST11 isolates showed less serum and phagocytic resistance than the serotype K1/K2 isolates. The mouse lethality test revealed that all ST11 isolates were unable to cause lethality, even at > 107 CFU, while serotypes K1 and K2 showed an LD50 at ≤ 103 CFU. Aerobactin or capsule knockout mutants exhibited a lower LD50 than the parental strain, while capsule mutants showed a more significant decrease in LD50.

Conclusion: Since there was a significant difference in virulence levels between the two types of HvKp when assessed in in vitro and in vivo models, it may be better to use the designation "HvKp" for some strains based on animal studies to avoid confusion. Virulence and non-virulence could be analysed in a relative manner, especially in comparison studies.

Keywords: Hypervirulence; Klebsiella pneumonia; MLST; Serotype.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
String test results for HvKp isolates with serotype K1/K2 and ST11 with serotype K20, K47 and K64. The mutants included ΔiucA, Δcps and ΔiucA/Δcps double mutants derived from a serotype K1/K2 isolate and a ST11 isolate with serotype K20
Fig. 2
Fig. 2
Neutrophil phagocytosis among HvKp from wild-type isolates of serotype K1/K2 and ST11 with serotype K20, K47 and K64 isolates
Fig. 3
Fig. 3
Neutrophil phagocytosis among HvKp-derived mutants from wild-type isolates. K1/K2 and ST11 isolates. The mutants included ΔiucA, Δcps and ΔiucA/Δcps double mutants
Fig. 4
Fig. 4
The mean lethal dose, i.e., the LD50, of wild-type HvKp isolates and their derived mutants in mice
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