50 STUDY AND IDENTIFICATION OF BACTERIA 



2. Divide irregularly. Bunch of grapes arrangement. (Staphylococci.) 



a. Gelatin not liquefied. M. cereus albus. 



b. Gelatin liquefied. / M. (Staphylococcus) pyogenes albus. 



\ M. (Staphylococcus) pyogenes aureus. 



c. Gelatin very slightly liquefied. 



S. epidermidis albus. (Stitch coccus.) 

 B. Cocci biscuit-shape. 



Diplococcus crassus. (May be mistaken for meningococcus.) 

 On ordinary agar we have a scanty growth resembling the streptococcus. 

 Colonies on ascites agar are smaller than those of meningococcus. It produces acid 

 in glucose, maltose and lactose. 

 II. Gram-negative cocci. 



A. Grow only at about incubator temperature. 



1. Grow only on blood or serum media. Gonococcus. 



2. Grow on blood serum media, or glycerine agar. 



a. Diplococcus intracellularis meningitidis. (Produces acid in glucose 

 and maltose but not in lactose.) 



3. Grows on ordinary media. Micrococcus melitensis. 



B. Will grow at room temperature as well as at 37 C. 



a. Micrococcus catarrhalis. Does not produce acid in glucose or maltose. 



b. M. pharyngis siccus. Colonies dry and tough and adhere to medium. 

 NOTE. Other biscuit-shaped Gram negative organisms resembling the meningo- 

 coccus are (a) Diplococcus flavus. The colonies show yellow pigment and we have 

 three varieties according to the depth of the yellow color, (b) M. pharyngis siccus 

 and (c) M. cinereus chiefly have coarse dry colonies on ascitic agar. 



STREPTOCOCCUS FORMS. 



Those cocci tending to arrange themselves in chains are usually 

 described as streptococci. (Ogston, 1881; Rosenbach, 1884.) 



When we consider that certain bacilli at times assume an arrange- 

 ment which we term strepto-bacilli, yet have no relationship, it would 

 suggest that the matter of chain morphology is simply a characteristic 

 common to many entirely different cocci. 



Again old laboratory cultures of streptococci may show alternations of cocci 

 and rods giving the appearance of the dots and dashes of the Morse code. Further- 

 more unsuitable media may bring about various involution types in an organism 

 primarily streptococcal. 



It is often difficult to distinguish streptobacilli from streptococci morphologic- 

 ally and the same is true of diplococci and diplobacilli. These bacillary pairs and 

 chains however often show bipolar staining and are almost invariably Gram 

 negative. 



While streptococci tend to assume chain formation in pus and tissues they often 

 appear as diplococci in blood. 



