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Virulence among different types of hypervirulent Klebsiella pneumoniae with multi-locus sequence type (MLST)-11,
Tsui-Chin Wang1, Jung-Chung Lin2, Jen-Chang Chang1
1National Institute of Infectious Disease and Vaccinology, National Health Research Institute, Zhunan, Miaoli, Taiwan.
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.
Insights
Hypervirulent Klebsiella pneumoniae (HvKp) strains, specifically ST11 and serotype K1/K2, exhibit distinct virulence levels. Serotype K1/K2 strains demonstrate significantly higher virulence and mouse lethality compared to ST11 isolates in comparative studies.
Area of Science:
- Microbiology
- Infectious Diseases
- Bacteriology
Background:
- Two main types of hypervirulent Klebsiella pneumoniae (HvKp), ST11 and serotype K1/K2, are recognized.
- Previous studies described these strains as HvKp but did not compare their virulence directly.
Purpose of the Study:
- To compare the virulence of ST11 and serotype K1/K2 HvKp strains.
- To elucidate the differences in virulence using in vitro and in vivo models.
Main Methods:
- Twenty-nine K. pneumoniae isolates (17 ST11, 6 K1, 6 K2) were analyzed.
- Phenotypic virulence tests, PCR for virulence genes, serum resistance, and phagocytosis assays were performed.
- Median lethal dose (LD50) in mice was determined after intraperitoneal injection.
Main Results:
- ST11 isolates showed lower serum and phagocytic resistance than K1/K2 strains.
- ST11 isolates did not cause lethality in mice (LD50 > 10^7 CFU), while K1/K2 strains had LD50 ≤ 10^3 CFU.
- Aerobactin or capsule gene knockouts reduced LD50, with capsule mutants showing a more significant decrease.
Conclusions:
- Significant virulence differences exist between ST11 and K1/K2 HvKp strains.
- The designation 'HvKp' may require refinement based on animal study data to avoid confusion.
- Virulence assessment should be relative, especially in comparative studies.
