Characterization of fumarate reduction by Klebsiella pneumoniae isolated from patients with chronic periodontitis

Chronic periodontitis is oral inflammatory gum disease which affects the tissues that support the teeth. It is caused by formation of bacterial plaque consisting of bacterial species that produces various virulence factors. Oral bacterial species from the periodontitis patients include species of Fusobacterium, Porphyromonas, Prevotella, Tannerella, etc. In the present study, we isolated the Klebsiella pneumoniae strain 9A from the pockets of patients suffering from chronic periodontitis. The strain was isolated on enriched tryptic soya media containing 10 mM fumarate and identified based on Gram staining, 16S rRNA gene sequencing, biochemical tests and ability to reduce fumarate. Our study is the first report of anaerobic fumarate reduction capabilities of Klebsiella spp. isolated from chronic periodontitis patients, which may help in growth and survival of species in periodontal pockets leading to progression of the disease. In addition, experimental evidence is provided through reduction, growth, and inhibitor assays for the presence of fumarate reductase (Frd) activities. Furthermore, we detected a 400 bp frdA gene fragment in Klebsiella pneumoniae strain 9A using degenerate PCR. This fragment show similarity to fumarate reductases flavoprotein subunit (FrdA). Our findings suggest that the FrdA subunit is responsible for anaerobic fumarate respiration in Klebsiella spp. to be important in the survival of bacteria in oxygen-deprived environments in humans such as periodontal pockets, thus contributing to its pathogenicity.