862 CLOSTRIDIUM 



Metabolism. — Up till within recent years it was generally believed that members 

 of this group were unable to grow except when oxygen was rigidly excluded from 

 the medium. Though free oxygen does inhibit their growth, and may actually 

 destroy organisms in the non-sporing state, it is quite possible to obtain growth 

 of anaerobic bacteria in the presence of air provided a sufficiently low oxidation- 

 reduction potential is established in the medium. This can be done by including 

 substances in the medium which will take up molecular oxygen and bring about a 

 fall in the Eh below that necessary for the initiation of growth. Many such sub- 

 stances are available, some of which act mainly by absorbing oxygen, others of which 

 are chiefly responsible for the establishment of a low Eh after the molecular oxygen 

 has been nearly used up or removed by mechanical means. Sulphites, reduced iron 

 compounds, unsaturated fatty acids, activated glucose, cysteine, glutathione, 

 ascorbic acid, thioglycoUic acid, and metallic iron are examples of some of the 

 substances commonly added to media to bring about the requisite anaerobic 

 conditions. Cooked meat is an example of a medium that affords excellent con- 

 ditions for anaerobic growth even when incubated aerobically. Its virtue Hes in 

 its containing (1) unsaturated fatty acids, which take up oxygen, the reaction 

 being catalysed by the haematin of the muscle, and (2) glutathione, which brings 

 about a negative 0-R potential corresponding to an Eh of about — 0-2 volt 

 (Lepper and Martin 1929, 1930). Fildes (1929) has shown that for the germina- 

 tion of tetanus spores an Eh in the medium approximating to + 0-01 volt at 

 pH 7-0 is required ; this corresponds to the zone of complete reduction of thionin. 

 It is probable that similar conditions determine the growth of most other anaerobes. 

 CI. histolyticum, CI. tertium and CI. carnis, however, are exceptions. These organ- 

 isms are microaerophilic rather than anaerobic, and can grow to a limited extent 

 aerobically, though they are said to be incapable of forming spores under these 

 conditions (Hall and Duffett 1935). Once growth has started, most anaerobic 

 organisms appear to bring about a rapid fall in the 0-R potential of the medium, 

 probably owing to the production of a more active reducing system than 

 that present in the medium itself. The Eh frequently falls to below — 0-4 volt. 

 According to Gillespie and Rettger (1938) the final Eh reached by the various 

 Clostridia in a given medium may be useful in species characterization. 

 As has just been pointed out, in the presence of powerful reducing systems growth 

 may continue even though considerable quantities of oxygen are gaining access 

 to the medium. 



We have discussed the exact nutritive requirements of certain Clostridia and 

 the problems of anaerobiosis at some length in Chapter 3. The earlier work of 

 Fildes and his colleagues (see Fildes 1935, Fildes and Knight 1933, Knight and 

 Fildep 1933, Fildes and Richardson 1935, Pappenheimer 1935, Knight 1936) and 

 of Stickland (1934, 1935) on essential nutrients of Clostridia and the modes of 

 their utilization has been developed to the point where it is clear that the majority 

 of pathogenic Clostridia are heterotrophs, requiring a battery of amiuo-acids, 

 carbohydrates, and vitamins for growth in artificial media. Moreover, the energy- 

 producing mechanisms, especially of those Clostridia that depend mainly on amino- 

 acid breakdown for their energy, have been studied in some detail (see, for example, 

 Gale 1940, Woods and Trim 1942, Clifton 1942, Guggenheim 1944). A small 

 concentration of COg seems to be as essential for the growth of the anaerobic 

 as it is for so many of the aerobic bacteria (Gladstone, Fildes, and Richardson 

 1935). In addition, the growth of some Clostridia is greatly improved by a con- 



