Bergey's Manual describes Streptococcus and Escherichia as faculative anaerobes How do the oxygen requirements of these organisms differ...Which one could correctly be called an aerotolerant anaerobe?

Answer 1

Streptococcus is an obligate anaerobe and therefore lacks catalase. However, Streptococcus would be considered an aerotolerant anaerobe because, even though it lacks catalase to break down hydrogen peroxide, it also lacks the cytochrome system that would produce hydrogen peroxide in the first place. Therefore, it is not aerobic, but it is tolerant of aerobic conditions.