Effect of Nitric Oxide on the Oxygen Metabolism and Growth of E. faecalis

Abstract

Summary Gastro-intestinal mucosal cells have a potent mechanism to eliminate a variety of pathogens using enzymes that generate reactive oxygen species and/or nitric oxide (NO). However, a large number of bacteria survive in the intestine of human subjects. Enterococcus faecalis (E. faecalis) is a Gram-positive bacterium that survives not only in the intestinal lumen but also within macrophages generating NO. It has been reported that E. faecalis generated the superoxide radical (O2 − ). To elucidate the role of O2 − and NO in the mechanism for the pathogen surviving in the intestine and macrophages, we studied the role and metabolism of O2 − and NO in and around E. faecalis. Kinetic analysis revealed that E. faecalis generated 0.5 µmol O2 − /min/10 8 cells in a glucose-dependent manner as determined using the cytochrome c reduction method. The presence of NOC12, an NO donor, strongly inhibited the growth of E. faecalis without affecting in the oxygen consumption. However, the growth rate of NOC12-pretreated E. faecalis in NO-free medium was similar to that of untreated cells. Western blotting analysis revealed that the NOC12-treated E. faecalis revealed a large amount of nitrotyrosine-posititive proteins; the amounts of the modified proteins were higher in cytosol than in membranes. These observations suggested that O2 − generated by E. faecalis reacted with NO to form peroxinitrite (ONOO − ) that preferentially nitrated tyrosyl residues in cytosolic proteins, thereby reversibly inhibited cellular growth. Since E. faecalis survives even within macrophages expressing NO synthase, similar metabolism of O2 − and NO may occur in and around phagocytized macrophages.

Antimicrobial Effects of Calcium Hydroxide and Chlorhexidine on Enterococcus faecalis

“…Additionally, chlorhexidine may induce reactive oxygen species production in the alkaline environment. The production of reactive oxygen species may inhibit E. faecalis growth because of the destruction of the cell wall and the plasma membrane mediated by nitric oxide (30). On the other hand, studies have reported that the antimicrobial activity of chlorhexidine is reduced when it is associated with Ca(OH) 2 (31).…”

Role of hydrogen generation by Klebsiella pneumoniae in the oral cavity

“…In fact, both oral bacteria and the infiltrating neutrophils exhibit significant amounts of oxidized proteins. The presence of this oxidative environment in the oral cavity means that not only pathogens, but also commensal bacteria, should have evolved antioxidant defense systems (Park et al, 2004;Sato et al, 2008;Nishikawa et al, 2009). In this study, both H 2 generation and the growth of K. pneumoniae were strongly inhibited by the presence of KCN and FeCl 2 plus H 2 O 2 , a hydroxyl radical generating system.…”

“…Antioxidant enzymes, such as superoxide dismutase and catalase, are components of these survival systems. A variety of bacteria living in the oral cavity and gastrointestinal tract, such as Helicobacter pylori, Streptococcus mutans, and Enterococcus faecalis, reduce the toxic effects of NO by generating superoxide radicals (Nagata et al, 1998;Nakamura et al, 2000;Sato et al, 2008;Nishikawa et al, 2009). Since superoxide, NO and peroxynitrite (a reaction product of these two radicals) play important roles in the oxidative damage of a variety of cells, these bacteria should have potent mechanisms for the reduction of oxidative stress caused by reactive species.…”

Heat-killed Enterococcus faecalis Alters Nitric Oxide and CXCL12 Production but not CXCL8 and CCL3 Production by Cultured Human Dental Pulp Fibroblasts

“…These findings might suggest an important role of NO in pulpitis and also in dental pulp calcification. In addition, the production of NO might be an important defense mechanism against E. faecalis because the growth of this microorganism is inhibited by NO in a reversible manner (40).…”