Effects of gallic acid on capsular polysaccharide biosynthesis in Klebsiella pneumoniae.

Abstract

Klebsiella pneumoniae is a gram-negative opportunistic pathogen that causes diseases mostly in immunocompromised individuals. Recently, hypervirulent K. pneumoniae strains also cause severe disease in healthy individuals. Capsular polysaccharide (CPS) is the major virulence determinant in hypervirulent K. pneumoniae and protects the cell against the bactericidal activity of the immune system. Gallic acid (GA), a natural phenolic compound, is known to exhibit wide spectrum antibacterial activity; however, its effect on hypervirulent K. pneumoniae remains largely unresolved. We aimed to identify the effects of GA on CPS biosynthesis in hypervirulent K. pneumoniae. Antibacterial activity of GA was evaluated by counting colonies. CPS amount was determined by glucuronic acid content. The transcriptions of cps gene cluster were measured by quantitative real time PCR (qRT-PCR) and the β-galactosidase activity. The effect of GA on the resistance of K. pneumoniae to streptonigrin (SNG), an iron-activated antibiotic, was evaluated. The effect of GA on the resistance of K. pneumoniae to serum killing and phagocytosis by macrophages was observed. GA inhibited the growth and CPS biosynthesis in K. pneumoniae. GA may affect the iron availability in K. pneumoniae, thus possibly repressing the cps transcription. In addition, GA reduced the resistance of K. pneumoniae to serum killing and enhanced its susceptibility to phagocytosis. GA possesses bactericidal activity and inhibits the CPS biosynthesis in hypervirulent K. pneumoniae, thereby facilitating pathogen clearance by the host immune system. Therefore, GA may represent a promising strategy for the prevention or treatment of patients with hypervirulent K. pneumoniae infections.