OBJECTIVETo investigate the effect of environmental oxygen on the inhibition between Streptococcus oligofermentans (So) and Streptococcus mutans (Sm) and the producibilities of hydrogen peroxide by So.

METHODSThe aerobic and anaerobic environment was established by the carbon dioxide cultivation. The inhibition between So and Sm was observed by plating method. The production and synthesis rates of hydrogen peroxide by So were determined in both aerobic and anaerobic environment by 4-ATTP-horseradish peroxidase method at A(510).

RESULTSWhen both Sm and So were inoculated at the same time, Sm was not inhibited under the anaerobic environment, vice versa. Sm was slightly inhibited by So under the aerobic environment, the inhibition area was 1/5 of all bacterial membrane. When So was cultivated first and then Sm applied, So could inhibite Sm growth under both anaerobic and aerobic conditions. The inhibition area was 1/5 of bacterial membrane under the anaerobic environment, and 4/5 under the aerobic environment. When Sm was cultivated first and then So applied, So was unable to proliferate under both conditions. During the logarithmic phase, the production of H2O2 by So under the aerobic environment was higher than under the anaerobic environment (P < 0.05). The initial synthesis rate of H2O2 by So during growth cycle under the anaerobic condition was (11.84 ± 3.97) µmol/L per minute, which was only 49% of that under the aerobic environment [(24.13 ± 4.46) µmol/L per minute].

CONCLUSIONSThe oxygen has the effect on the inhibition between So and Sm, and the inhibition in the aerobic environment is much stronger than in the anaerobic environment. The synthesis ability of hydrogen peroxide by So under the aerobic environment is higher than under the anaerobic environment.