C. ACNES 471 



Growth. — The type of growth on serum, agar, and gelatin appears to be very like 

 that of C. diphtherice. Pellicle formation in broth has not been recorded, but suitable 

 conditions have perhaps never been secured. 



Biochemical Reactions. — Acid is produced from dextrose, maltose, and saccharose ; 

 galactose, dextrin, lactose, and mannitol are unchanged. Litmus milk is unchanged, or 

 shows a slight and transitory acidity. Indole is not formed. Gelatin is not liquefied. 

 Nitrates are reduced. 



Antigenic Structure.- — ^At present uninvestigated. 



Toxin Production and Pathogenicity. — C. murium is a natural pathogen of mice, 

 and appears to be pathogenic for no other species, with the possible exception of rats. 

 There is evidence that some of its efifects are due to the action of a soluble toxin (see above). 



C. acnes 



A diphtheroid organism was described in the ordinary lesions of cutaneous acne by 

 Unna in 1896, and was isolated in culture by Sabouraud (1897). 



Morphology. — This has been 

 generally reported as very variable, r ^ .v*^iv» 



according to the medium employed, '^- i. P 



V 



degree of acidity, oxygen pressure, etc. - * '^^ ■« *-r^W 



Craddock (1942) distinguishes two /f^' *5^i^u ' ' ""^It V 



types on blood agar: in large colonies -,' ^>.''\'*' ~^S*fl^^' 



the organisms are short, thick, irreg- >-^'^^ ^\^ j,r ^^fj^^ 



ular in shape, and often clubbed ; in 



small colonies the bacilli are longer, ^m» 



thinner and curved. Often weakly " '/ 



Gram-positive. 



Growth. — C. acnes will grow aero- 

 bically if the medium contains serum 



or blood, and is acidified by the -m^ -y , "^ tt*^ /■ta 



addition of lactic, or of hydrochloric ^•''■*' '\-*-!^^'*^'^^-"* 



acid, so as to fall within the pH range "^ ' \ V*^***^ ^ 



6-2-6-8. Growth occurs better under '^'t^i^^h' 



anaerobic conditions, and is favoured " z'/.^ 



by glucose, glycerol, blood, boiled Fig. 87.— C. murium. 



blood, Fildes' extract of blood, and From 24-hours' cillture on Loeffler's serum ( x 1000). 

 serum. On plain agar growth is poor 



or absent. On a glucose agar plate anaerobically after 4 days at 37° C. the colonies 

 are circular, 0-2-0-4 mm. in diameter, convex, amorphous, greyish-white, with a smooth 

 glistening surface and an entire edge ; they are butyrous in consistency, and emulsify 

 easily. The growth has a sour smeU. After 6 weeks, colonies may be coloured pink. 

 On blood agar anaerobically Craddock (1942) describes two types : Type I forms a 

 large heaped-up colony, yellowish-buff in colour, with a wide zone of ha?molysis ; Type II 

 forms a small flat colony. In a glucose agar shake medium no growth occurs for 

 about 10 mm. below the surface ; there is then often a band growth for 10-20 mm. below 

 the surface, with discrete colonies to the bottom of the tube ; the medium becomes 

 milky and opaque. Loeffler's serum, no liquefaction. In glucose broth there is a slight 

 turbidity after 3 days anaerobically, and a slight, finely granular sediment ; after a week 

 or so there is a heavy loose floccular deposit, which occupies the lower centimetre of the 

 tube and disintegrates on shakmg to give a moderate turbidity. Slight to moderate 

 turbidity in cooked meat medium. No growth in gelatin stab culture at 22" C. 



Biochemical Reactions.— According to Siidmersen and Thompson (1909-10) C. acnes 

 produces acid from glucose, galactose, maltose, glycerol, and mannitol, but does not 



