Oxygen and „strictly anaerobic”︁ intestinal bacteria I. Effects of dissolved oxygen on growth

Abstract

AbstractThe effects of oxygen on 29 strains of „strictly anaerobic„ bacteria, which are often found in human intestinal tracts, were studied. The initiation and rate of growth, together with the maximum extent of growth, in sealed L‐shaped tubes containing a medium through which a gas mixture containing 5% O2 had been bubbled were compared with those under anaerobic conditions. On the basis of the results, these anaerobic bacteria could be divided into three general types: Type A; strains which grew in almost the same way as under anaerobic conditions, type B; strains which grew less well than under anaerobic conditions, and type C; strains incapable of growth initiation in the initial presence of the dissolved O2. After the experiments no residual O2 was found in the medium of type A strains. The decrease in O2 concentration was small, if any, in media of type B and C strains.Using representative examples of these three types, physical changes in the culture medium accompanying growth were observed in a stirred fermenter equipped with three electrodes; Eh, oxygen, and pH. The results were as follows: Type A: Growth of Veillonella alcalescens in the fermenter started after the complete comsumption of dissolved oxygen and when Eh had dropped below ‐ 300 mV. A slight drop in pH occurred in parallel with the growth. Type B: In the culture of Bifidobacterium adolescentis, growth was simultaneous with the changes in O2 concentration, Eh, and pH. Type C: Growth of Bacteroides vulgatus was not initiated in the presence of the dissolved O2. Little change in O2 concentration, Eh or pH was observed.When bacterial cells which had grown in the medium initially containing dissolved O2 were subjected to serial transfer to similar fresh media, growth activity appeared to decrease progressively.