Advances in Natural Sciences, T. 7, S. 1 (2006)

Cỡ chữ:  Nhỏ  Vừa  Lớn

Zinc Effects on Oxidative Physiology of Oral Bacteria

Nguyen Thi Mai Phuong, Phan Tuan Nghia, Robert E. Marquis

Tóm tắt

Zinc is used as an anti-gingivitis agent in oral care products and affects multiple targets
in oral bacteria. We found that it acts also to suppress respiration of oral streptococci and of
Fusobacterium nucleatum, an organism associated with development of gingivitis. Zinc as either
the sulfate or citrate chelate was a potent inhibitor of respiration of the oral streptococci Streptococus
mutans GS-5 or UA 159 and S. sanguis NCTC 10904. 50% inhibitory concentrations for
intact cells in suspensions were below 0.3 mM with nearly complete inhibition of O2 metabolism
at higher zinc levels. 1.0 mM Zn2+ inhibited O2 utilization by F. nucleatum ATCC 25586 by some
50%, but almost 40% of O2 metabolism by the anaerobe was not Zn sensitive. NADH oxidase
plays the major role on O2 utilization by oral streptococci and is also important for F. nucleatum.
In cell extracts of streptococci, the 50% inhibitory concentration (IC50) of Zn2+ for NADH oxidase
activity ranged from ca. 2.1 mM for S. sanguis NCTC 10904 to 3.0 mM for the GS-5 strains of S.
mutans. The enzyme in extracts of F. nucleatum was somewhat more Zn sensitive with an IC50
value of 1.4 mM. S. sanguis is a major generator of H2O2 in dental plaque. Zn2+acted to reduce
peroxide production assessed with use of horseradish-peroxidase and leuco-crystal violet. 0.1 mM
ZnSO4 was more than 50% inhibitory for cells in suspensions or mono-organism biofilms. Zinc is
primarily bacteriostatic rather than bactericidal, and inhibition was at least partially reversible
after zinc removal. Zinc was inhibitory also for the protective enzymes thiolperoxidase (IC50= 0.1
mM), hypothiocyanite reductase (IC50 = 0.1 mM) and glutathione reductase (IC50 = 0.4 mM).
Zinc acted mainly as a pro-oxidant for oral bacteria inhibiting NADH oxidase, considered to be
protective against oxidative stress, and also other protective enzymes. This view is supported by
findings of zinc enhanced peroxide killing of the organisms.
Abbreviations. Reactive oxygen species (ROS), NADH oxidase (NOX), NADH hypothiocyanite
reductase (NHOR), glutathione reductase (GR), thiolperoxidase (TSA), catalase (CAT), pseudocatalase
(PCAT), superoxide dismutase (SOD), 50% inhibitory concentration (IC50).