OxyFile #224

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


Author:  Ryan CS; Kleinberg I

Source:  Arch Oral Biol 1995 Aug; 40(8):753-63

Abstract:  

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.