372 MANUAL OF DETERMINATIVE BACTERIOLOGY 



Genus III. Propionibacterium Orla-Jensen* 



(Cent. f. Bakt., II Abt., 22, 1909, 337.) From M. L., propionic, and bacterium, a 

 small rod or stick. 



Non-motile. Non-spore -forming. Gram-positive bacteria growing under anaero- 

 bic conditions in neutral media as short diphtheroid rods, sometimes resembling 

 streptococci ; under aerobic conditions with heavy inoculum growing as long, irregular, 

 club-shaped and branched cells. Metachromatic granules demonstrable with 

 Albert's stain. Ferment lactic acid, carbohydrates, and polyalcohols with the forma- 

 tion of propionic and acetic acids and carbon dioxide. As a rule strongly catalase 

 positive, sometimes weakly so. Strong tendency towards anaerobiosis ; development 

 very slow, macroscopically visible colonies generally not discernible in less than 5 to 

 7 days.f Nutritional requirements complex. Development best in yeast extract 

 media with addition of lactates or simple carbohydrates. Optimum temperature 

 30°C. Found in dairy products, especially hard cheeses. 



The type species is Propionibacterium freudenreichii van Niel. 



Key to the species of genus Propionibacterium. 



I. In yeast extract-glucose media growth occurs in the form of small streptococci- 

 Dirty cream-colored growth in stabs, with slight surface growth of same color. 

 Sucrose and maltose not fermented. 



A. Not fermenting lactose. 



1 . Propionibacterium freudenreichii. 



B. Fermenting lactose. 



2. Propionibacterium shermanii. 



II. In yeast extract-glucose media growth occurs in the form of typical short rods of 

 diphtheroid appearance. Distinct surface growth in stabs. Sucrose and 

 maltose are fermented. 



A. Growth brownish-red. 



1. Ferments raffino.se and raannitol, but not sorbitol. 



3. Propionibacterium rubrum. 



2. Ferments sorbitol, but not raffinose and mannitol. 



4. Propionibacterium thoenii. 



B. Growth in stab cream-colored. 



1. Surface growth cream-colored. 



a. Ferments 1-arabinose and rhamnose. 



5. Propionibacterium zeae. 



2. Surface growth yellow to orange. 



a. Growth in liquid media flocculent, as if agglutinated. 



6. Propionibacterium. peterssonii. 

 aa. Growth in liquid media dispersed, smooth. 



* Revised by Prof. C. B. van Niel, Hopkins Marine Station, Pacific Grove, Cali- 

 fornia, June, 1938; further revision by Prof. Van Niel, January, 1944. 



t In an atmosphere containing 5 per cent carbon dioxide, growth is enhanced both 

 aerobically and anaerobicall^^ Contrary to the claim made Vjy Krebs and Eggleston 

 (Biochem. Jour., 3-5, 1941 , 676) a differential effect of carbon dioxide tension on aerobic 

 and anaerobic development has never been observed. 



