Susceptibility of Porphyromonas gingivalis and P. asaccharolytica to the non-oxidative killing mechanisms of human neutrophils

Abstract

Neutrophils are essential for host defence against bacterial dental plaque and the pathogenic bacterial species within it, but in anaerobic environments such as the gingival crevice neutrophils can kill bacteria only with non-oxidative microbicidal compounds stored in their granules. Porphyromonas gingivalis W83, a pathogenic plaque species, and the avirulent non-oral type-strain P. asaccharolytica were incubated anaerobically with intact neutrophils and with compounds extracted from normal human neutrophil granules. The killing of bacteria and the inactivation of lysozyme, cathepsin G, elastase, bacterial-permeability increasing factor and defensins by culture supernatants were assayed. P. asaccharolytica but not P. gingivalis was killed under anaerobic conditions by intact neutrophils. P. gingivalis was also resistant to neutrophil granule compounds, its viability being reduced from a mean of 3.3 × 10 6 to 6.1 × 10 4 c.f.u/ml in 60 min by 400 μg/ml neutrophil granule extract, as compared to a reduction from 4.4 × 10 6 to 2.3 × 10 3 c.f.u/ml for P. asaccharolytica, P. gingivalis culture supernatant inactivated cathepsin G, elastase, bacterial-permeability increasing factor and defensins. Resistance to neutrophil non-oxidative killing mechanisms may be an important virulence factor for P. gingivalis.