Abstract
Actinobacillus actinomycetemcomitans and the genetically-related oral haemophili ( Hae mophilus segnis, Haemophilus aprhophilus and Haemophilus paraphrophilus) exhibit a range of sensitivities to the lethal effect of hydrogen peroxide (H 2O 2), A. actinomycetemcomitans being the most resistant. To extend this information, susceptibility to a range of H 2O 2 concentrations (10 −6-10 −3 M) was assessed by incubating bacterial suspensions for l h at 37°C in the presence of H 2O 2 and spreading the suspensions on chocolate agar plates to determine the concentration of H 2O 2 producing a 50 per cent reduction in colony-forming units (LD 50). Catalase activity was quantified with a dark-type oxygen electrode, which polarographically monitored the formation of dissolved oxygen in bacterial suspensions or sonicates following addition of reagent H 2O 2. Sensitivity to H 2O 2 did not correlate with catalase activity, either in intact cells or in bacterial sonicates. Specifically, some bacterial strains with undetectable catalase activity were highly resistant to H 2O 2. Micromolar concentrations of sodium azide which completely inhibited cell-associated catalase activity did not affect the resistance of A. actinomycetemcomitans to H 2O 2. Thus, the endogenous catalase activity of A. actinomycetemcomitans and certain oral haemophili is not an important determinant of resistance to the bactericidal effects of H 2O 2.
Published Version
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