466 



COR YNEBACTERI UM 



On tellurite blood agar plates, the colonial differences that characterize the gravis, 

 mitis and intermediiis types (see Table 30) can most readily be observed. These colonial 

 differences are, however, also observable on certain other media, such as trypsin serum- 

 agar (Dudley et al. 1934). 



Broth. See Table 30. 



C. diphtherice is aerobic and facultatively anaerobic. 



The optimum temperature for growth is in the near neighbourhood of 37° C. ; with 

 a range from about 15° to 40° C. over which growth occurs. 



Heat resistance is slight, a temperature of 58° C. for 10 minutes sufficing to sterilize 

 a suspension or broth culture. 



Biochemical Reactions. — C. diphtherice ferments glucose, galactose, and maltose, 

 with the production of acid but no gas. It has no action 

 on saccharose, lactose or mannitol. Litmus milk is unchanged. 

 Indole is not formed ; but, according to the results obtained by 

 Frieber (1921), C. diphtherice gives a colour reaction with sulphuric 

 acid and potassium nitrite as a result of the formation of indole- 

 acetic acid from tryptophan. This substance does not, however, 

 give the colour reaction with paradimethylamidobenzaldehyde 

 which is characteristic of indole itself. Nitrates are reduced. 

 Gelatin is not liquefied. 



The gravis type, in addition to the carbohydrate substrates 

 referred to above, ferments dextrin, starch and glycogen. The 

 mitis and intermedins ty^ea give irregular results with dextrin 

 and do not ferment starch or glycogen. 



The mitis type is usually hsemolytic, the gravis type is usually 

 non-hsemolytic, and the intermedins type is consistently non- 

 hsemolytic. 



Antigenic Structure. — C. diphtherice is divisible into a 

 number of different antigenic types. The gravis, mitis and inter- 

 medins types differ antigenically from each other, and each is 

 divisible into a number of antigenic sub-types. 



Toxin Production and Pathogenicity. — C. diphtherice is 

 pathogenic for man and for certain laboratory animals. It pro- 

 duces a powerful exotoxin with a characteristic action on the 

 animal tissues (see above). Non-virulent strains of the mitis type 

 are not uncommon. 



Fig. 



diph- 



85.— C. 

 therice. 



24-hours' culture on 

 Loeflfler's serum. 



C. hofmanni 



Von Hofmann, in 1888, isolated from the throats of normal persons a diphtheroid 

 bacillus which was probably identical with the species which now bears his name. The 

 incompleteness of the earlier descriptions does not allow us to identify with any certainty 

 the various strains which were, about this time, described under the general head of 

 " pseudodiphtheria bacilli." The description which follows refers to a particular type of 

 diphtheroid bacillus to which the name of C. hofmanni has been allotted by common con- 

 sent. There are other forms of non-fermenting diphtheroid bacilli which possess quite a 

 different morphology. These must, for the moment, be left unnamed, finding a temporary 

 home in the appropriate groups of the fermentative types differentiated by the Committee 

 of the Medical Research Council. 



Morphology. — Short rods, 1 -5 to 2 /i in length, with parallel sides, rounded or slightly 

 pointed ends, with a straight axis, and a single unstained central septum. Metachromatic 

 granules are usually absent ; if present they are few in number, small and inconspicuous. 

 There is little or no tendency to pleomorphism. The bacilH are arranged in parallel 

 rows, or in irregular groups, with the usual angular displacement of adjacent cells (see 



