A Review of the Innate Immune Evasion Mechanisms and Status of Vaccine Development of Klebsiella pneumonia

Klebsiella pneumoniae (KP) is a human pathogen causing a broad spectrum of diseases such as urinary tract infections (UTI), pneumonia, pyogenic liver abscess, bloodstream infections, and sepsis. Neonate, geriatric and immunocompromised individuals are the most vulnerable to KP infections. The success of KP as an infectious agent is due to the evolution of various mechanisms to evade the host's immune system. These diverse mechanisms have led to the dominance of KP infections in community settings where hypervirulent strains predominate and in hospital-acquired infections where multidrug-resistant strains predominate. KP infections in the past decades have been increasingly associated with high morbidity and mortality due to the emergence of multidrug-resistant and hypervirulent strains capable of evading both the internal immune defense mechanisms and external antimicrobial agents. The pharmaceutical industries have very few and often expensive new antibiotics in the pipeline, offering little hope for antibiotic therapy. The development of new therapeutic strategies such as polyvalent, biconjugate vaccines that can provide protective immunity, especially against vulnerable populations, can mitigate the effects of KP infections. In this review, we discuss the virulence mechanisms of KP and how it evades the innate host immunity, and the interplay between the virulence and immune evasion strategies. The progress in the search for a vaccine to protect against KP infections will also be highlighted.