CHAPTER V. 



STUDY AND IDENTIFICATION OF BACTERIA COCCI. KEY 



AND NOTES. 



Streptococcus Forms. Cells, divide to form chains. 



I. Gelatin not liquefied. 



1. Haemolytic zone on blood agar. 



a. Very slight acidity in lactose litmus bouillon. S. pyogenes. Tends to 

 produce arthritis in experimental animals. Often a granular sediment in 

 bouillon. 



b. Marked acidity but no gas production in lactose litmus bouillon. S. 

 acidi lactici. Non pathogenic. Forms diffuse cloudiness in bouillon. 



2. Greenish appearance about colonies on blood agar. 



a. No tendency to capsule formation. S. viridans. Produces endocarditis 

 in experimental animals. 



b. Distinct capsule formation in pathological material or on favorable media. 

 S. lanceolatus (Pneumococcus). Gram positive, lance-shaped cocci with 

 bases apposed within a capsule. 



c. Very marked capsule development on all media. S. mucosus. A. strepto- 

 coccus with extraordinary capsule development, up to io(i in width, S. 

 mesenterioides, is not pathogenic. 



II. Gelatin liquefied. 



Streptococcus coli gracilis. (Cocci quite small 0.2 to 0.4/1. In faeces.) 

 A tube-like liquefaction, chains rather long; only slight growth on agar. 



Constant inhabitant of stools of meat diet. 

 Sarcina Forms. Cells divide in three dimensions of space. (Packets). 



A. No pigment production on agar. 



a. Sarcina alba. (Colonies finely granular.) 



b. Sarcina pulmonum. 



B. Yellowish pigment. 



a. Sarcina lutea. (Colonies coarsely granular.) 



b. Sarcina flava. (Colonies finely granular.) 



C. Rose-red pigment. 



a. Sarcina rosea. 



Micrococcus Forms. Cells divide irregularly in various directions. 

 I. Gram-positive cocci. 

 A. Cocci round. 



i. Divide in two planes at right angles. Tetrad formation. Merismopedia. 

 a. M. tetragenus. Moist white viscid colones. No liquefaction of 

 gelatin. Capsule. 



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