OxyFile #428

Bacteria in human mouths involved in the production and 
utilization of hydrogen peroxide.

Ryan CS; Kleinberg I

Department of Oral Biology and Pathology, State University of New 
York, Stony Brook 11794-8702, USA.

Arch Oral Biol, 40: 8, 1995 Aug, 753-63


Earlier studies have demonstrated that pure cultures of oral 
streptococci produce hydrogen peroxide but none has found any free 
peroxide in dental plaque or salivary sediment despite 
streptococci being major components of their mixed bacterial 
populations. The absence of peroxide in plaque and sediment could 
be due to the dominance of its destruction over its formation by 
bacterial constituents. To identify which of the oral bacteria 
might be involved in such a possibility, pure cultures of 27 
different oral bacteria were surveyed (as well as dental plaque 
and sediment) for their peroxide-forming and peroxide-removing 
capabilities. Peroxide production was measured for each of the 
pure cultures by incubation with glucose at low and high substrate 
concentrations (2.8 and 28.0 mM) for 4 h and with the pH kept at 
7.0 by a pH-stat. Removal of hydrogen peroxide was assessed in 
similar experiments where peroxide at 0, 29.4, 147.2 or 294.4 mM 
[0, 0.1, 0.5 and 1% (w/v)] replaced the glucose. Hydrogen peroxide 
formation was seen with only three of the bacteria tested, 
Streptococcus sanguis I and II (sanguis and oralis), and Strep. 
mitior (mitis biotype I); levels of hydrogen peroxide between 2.2 
and 9.8 mM were produced when these micro-organisms were grown 
aerobically and 1.1 and 3.9 mM when grown anaerobically. Earlier 
reports indicate that such levels were usually sufficient to 
inhibit the growth of many plaque bacteria. The amounts formed 
were similar at the two glucose levels tested, suggesting that 
maximum peroxide production is reached at low glucose 
concentration. None of the three peroxide-producing organisms was 
able to utilize hydrogen peroxide but five of the other 24 tested, 
Neisseria sicca, Haemophilus segnis, H. parainfluenzae, 
Actinomyces viscosus and Staphylococcus epidermidis, could readily 
do so, as could the mixed bacteria in salivary sediment and dental 
plaque, both of which contain relatively high numbers of these 
peroxide-utilizing micro-organisms. The ability of the bacteria in 
plaque and sediment to degrade hydrogen peroxide was considerable 
and extremely rapid; peroxide removal and usually complete within 
the first 15 min of the incubation even when its initial level was 
as high as 294.4 mM. This almost overwhelming ability to remove 
peroxide was confirmed when peroxide-producing and -using cultures 
were mixed and when each of eight salivary sediments was incubated 
with glucose and with peroxide at concentrations up to 294.4 mM. 
In the glucose incubations, no hydrogen peroxide was observed, 
indicating dominance of microbial peroxide removers over hydrogen 
peroxide producers.