452 CORYNEBACTERIUM 



though the evidence on this point is somewhat conflicting. Concerning the resist- 

 ance of the various species of diphtheroid bacilli we have far less precise informa- 

 tion ; such data as are available suggest that they behave, in this respect, in much 

 the same way as the type species. An exception must, however, be made for 

 C. equi, which is reported by Karlson, Moses and Feldman (1940) to be unusually 

 resistant to certain chemical disinfectants like oxalic acid that are used in the 

 cultivation of tubercle bacilli from contaminated material. Most vegetative 

 organisms are destroyed within 15 minutes by exposure to 1-5 per cent, oxalic 

 acid ; C. equi is said to resist even a 5 per cent, solution for an hour. 



Metabolism and Growth Reauirements. 



The oxygen requirements of different species within this genus vary widely. 

 Though all species are apparently able to grow in the absence of gaseous oxygen, 

 some species, including C. dipJitJieriw itself, develop far more freely under aerobic 

 conditions, and display this preference by growing as a film or veil over the surface 

 of a liquid medium. Other species, such as C. acnes and C. typhi, are microaerophilic. 



The temperature range over which most members grow in artificial media 

 extends from about 15° to 40° C, with an optimum at about 37° C. 



It has already been pointed out that the growth of all species is improved 

 by the addition of a natural animal protein to the medium. Both blood and 

 serum favour growth, but some members, particularly the mitis type of C. diphthericB, 

 are inhibited by heated blood, as well as by blood treated by acid or alkali. Accord- 

 ing to Glass (1939a, b) this effect is apparent only in aerobic culture, and is abolished 

 by the addition of sodium hydrosulphite or by anaerobic cultivation. 



So far as growth on synthetic media is concerned, our information is as yet relatively 

 scanty, in spite of a considerable mass of experimental data (see Uschinsky 1893, 1897, 

 Hadley 1907, Hadley and Gorham 1907, Koser and Rettger 1919, Davis and Ferry 1919, 

 von Groer 1923, Hosoya and Kuroya 1923, Robertson 1924, Braun and Hofmeier 1927, 

 Braun and Miindel 1927, 1929, Braun, Hofmeier and Miindel 1929, Maver 1930, Lindemann 

 1932, Ehrismann 1932-33, 1933, Hottinger and Hottinger 1933, Nitsch 1933, Schmidt 

 1933-34, Wadsworth and Wheeler 1934, Knight 1936). It may be summarized by noting 

 ( 1 ) that C. diphtherice appears to be incapable of growth with ammonia as the sole source 

 of nitrogen, carbon being supplied in an organic form ; (2) that growth, and toxin produc- 

 tion, often occur when amino-acids are added to such a synthetic medium, and that, 

 among these amino-acids, cystine, aspartic acid and perhaps trj^ptophan appear to be 

 indispensable ; and (3) that it is only certain " non-exacting " strains that are capable of 

 growing in such a medium, and even with these strains toxin production is usually much 

 less abundant than with a more adequate food-supply. Knight (1936) emphasizes the 

 difficulty of assessing the real significance of many of the recorded findings in view of the 

 great difficulty of obtaining most ammo-acids in a state of chemical purity. 



Attempts have been made (Bunker 1919, Hosoya et al. 1933, MueUer et al. 1933, Mueller 

 1935a, b, c) to identify the additional substances required for active growth and toxin 

 production by fractionating peptone, meat extract and other types of complex protein 

 extracts or hydrolysates in which C. diphtherice is known to grow abundantly. Considerable 

 progress has been made along these lines (see Chapter 3). 



Biochemical Reactions. 



The carbohydrates most frequently employed as test substrates for the differentia- 

 tion of species within this genus are dextrose, maltose and saccharose. The type 

 species, C. diphtherice, produces acid but no gas in dextrose and maltose, but does 

 not attack saccharose. Other species, such as C. xerosis produce acid in all three 



