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

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.

Clinical Outcomes and Microbiological Characteristics of Sequence Type 11 Klebsiella pneumoniae Infection

“…Further investigations are required to determine whether genetic deletion has a potential effect on the hypervirulence phenotype. Previous studies demonstrated that the K1 and/or K2 capsule serotypes were commonly associated with enhanced virulence ( 36 , 37 ). However, none of the MDR hvKp strains possessed the K1/K2 serotype in this study.…”

Phenotypic and Genotypic Characterization of a Hypervirulent Carbapenem-Resistant Klebsiella pneumoniae ST17-KL38 Clinical Isolate Harboring the Carbapenemase IMP-4

“… Klebsiella pneumoniae is a well-studied Gram-negative bacterium of the Enterobacterales family and a prominent cause of community-acquired and nosocomial infections ( 1 – 3 ). Globally distributed antimicrobial-resistant clones, particularly carbapenem-resistant K. pneumoniae (CRKP), pose serious therapeutic challenges ( 4 ).…”

Epidemiology, Environmental Risks, Virulence, and Resistance Determinants of Klebsiella pneumoniae From Dairy Cows in Hubei, China

“…At present, the hvKP was reported to be most common in K. pneumoniae with ST11, serotype K1 or K2 ( Wang et al, 2021 ). No strains of these serotypes and sequence types were found in this study, but K54 ( wzi 66, wzi 115, n = 2) and K57 ( wzi 57, n = 1) were found, which may also be related to high virulence ( Zhong et al, 2020 ).…”