Chapter III — 59 — Morphology 



duced by die splitting off of the tip of the hvpha. The conidia are 

 spherical (1.0-1. 3[jl in diameter), oval, or oblong (1.3-1.5 X 1-2ijl). 

 Sporulation occurs most abundantly on synthetic media. 



Types of Growth on Solid and Liquid Media:— 



Aerobic organisms.— The colonies of the aerobic actinomycetes, con- 

 sidered by some as pseudo-colonies, differ greatly from the colonies of 

 fungi, on the one hand, and of the bacteria, on the other. They are 

 usually compact, leathery, growing deep into the medium. Only cer- 

 tain few aerobic pathogens produce colonies of a dough-like con- 

 sistency, which makes them similar to the colonies of bacteria. 



The colonies can be round and smooth, or much-folded, lichnoid to 

 almost barnacle-like in appearance. The edge of the colony, when 

 examined under the microscope, gives a characteristic picture of radiat- 

 ing hyphae. The colony may be produced below or on the surface of 

 the medium. In liquid media, the colonies may be formed individually 

 on the bottom of the container, they may adhere to the surface of the 

 wall of the container, or they may give rise to a ring of growth on the 

 surface of the medium. The surface colonies may coalesce, producing 

 a pellicle of varying degrees of compactness. The colonies may also 

 be flaky in appearance, but they cause no turbidity of the medium. 

 Sometimes the surface growth is similar to that of tubercle bacteria, that 

 is, dough-like and folded, without producing any aerial mycelium. The 

 composition of the medium has an influence upon the nature of the 

 growth. 



When actinomycetes are grown in a submerged or in a shaken con- 

 dition (452, 517) they produce characteristic small, bead-like colonies, 

 or granules which may completely fill the culture vessel. Probably be- 

 cause of the continuous break-up of the mycelium or the separation of 

 the spores, growth is much more rapid and more abundant in sub- 

 merged culture than in stationary culture. This is particularly true 

 of certain species of Microvionospora. 



Anaerobic organisms.— The morphology of the anaerobic forms repre- 

 sents a special problem. Erikson (112) made a detailed study of the 

 morphology of 1 5 strains of the microaerophilic types of A. bovis derived 

 from human materials and of 5 strains of bovine origin. 



A very sparse development of erect aerial hyphae was detected 

 when the human strains were grown in an atmosphere of reduced 

 ox)^gen tension. These hyphae were found to be occasionally septate, 

 but no definite spores were produced; they were of the same diameter 

 as the hyphae of the substratum mycelium. The substratum mycelium 

 is initially unicellular, the branches extending into long filaments, caus- 

 ing the colony to adhere to the medium. This mycelium may give rise 

 to irregular segments, with a characteristic angular branching. The 

 colonies were said to exhibit polymorphism, although no stable variants 

 could be demonstrated. They gave no turbidity in the medium. 



