Oxygen tolerance of anaerobic bacteria isolated from necrotic dental pulps

The oxygen tolerance of 43 anaerobic reference strains and 36 anaerobic strains from necrotic dental pulps was studied. All strains survived for two hours or more as colonies on the surface of a medium supplemented with blood, and as many as 26 of the 79 strains survived for more than seven days. The hemolysed blood in the medium significantly increased the survival time for many of the strains. Factors influencing the death rate were studied in one of the strains and it was found that the lysed red cells of the blood and not the serum had a protective effect and that catalase had the same protective effect as the hemolysed blood. The finding that hemolysed blood significantly increased the oxygen tolerance of many anaerobes may explain some of the divergent results regarding the efficiency of various methods for the recovery of anaerobic bacteria from clinical specimens. The use of media supplemented with blood during various phases of processing a specimen might be more important for a high recovery of anaerobic bacteria from clinical sources than the measures taken to minimize exposure of the specimen to air.