380 ACTINOMYCES 



1940) ; in liquid media there is sometimes a slight turbidity, and a wispy or Ught 

 flocculent deposit ; mannitol and salicin are seldom fermented ; and antigenically 

 they constitute a separate group. 



Classification 



Lieske (1921), who made an extensive study of the Actinomyces from the point 

 of view of a botanist, found so much variation in the behaviour of individual strains 

 that he was unable to arrive at any satisfactory classification. Subsequent workers, 

 however, have felt that Lieske overestimated the difficulties of this task. Attempts 

 at classification have been made along both morphological and physiological lines. 

 The most prominent exponent of the former group during recent years is 0rskov 

 (1923), who devised the following scheme : 



Group I. " Spores " give rise to a unicellular branching mycelium. This 

 affords the substratum for an aerial mycelium, which consists of rather thicker- 

 branched filaments. " Spores " are formed from the aerial hyphae without any 

 previous segmentation of the cytoplasm. " Spore " formation commences at the 

 tip of the thread and proceeds towards the base. " Spores " are more resistant 

 to heat than the plain mycelia. Minor points are that the primary mycelium is of 

 cartilaginous consistency, and often sends roots into the agar. The aerial mycelium 

 may arise centrally or peripherally, and may not appear for a long time. Condensa- 

 tion of the cytoplasm occurs at regular intervals. Whole appearance of organism 

 is fairly uniform. Gelatin is often liquefied. This group seems to include most 

 of the non-acid-fast aerobic species. 



Group II A . Both the primary and the aerial mycelium are of the same diameter, 

 and both undergo early segmentation into irregular fragments. The aerial mycelium 

 arises very early in the culture. It starts at the centre of the primary mycelium 

 and spreads concentrically towards the periphery. No " spore " formation occurs, 

 and the segmented mycelial fragments are no more resistant to heat than the 

 unicellular mycelium. The whole appearance is very pleomorphic ; coccoid, 

 bacillary, filamentous, clubbed, and irregular-shaped forms are common. The 

 growth is generally soft in consistency, and does not adhere to the medium. A 

 reddish insoluble pigment is frequently formed. Gelatin is not usually liquefied. 

 This group includes many of the aerobic acid-fast species, such as Actinomyces 

 asteroides and Actinomyces farcinicus. 



Group IIB. Differs from Group IIA in forming no aerial mycelium. [Erikson 

 (1935), however, denies this, and would do away with the distinction between the 

 A and B groups.] Besides segmentation, the so-called angular division is common 

 in this sub-group, and is responsible for the diphtheroid appearance of these 

 organisms in film preparations. Group IIB comprises mainly the anaerobic species, 

 of which the most important is the pathogenic organism described by Wolff and 

 Israel. 



Group III. The characteristic feature of this group is the formation of oval 

 " spores " at the extreme tips of the mycelial branches. No aerial mycelium is 

 produced. Only one species has so far been recognized — Actinomyces clialcece. 



Naeslund (1925) put forward a classification based primarily on physiological 

 characteristics. We have modified it very slightly, and present it in the following 

 form, paying attention mainly to the organisms that are parasites or potential 

 parasites of animals. 



