60 MEDICAL BACTERIOLOGY 



Schottmiiller has employed this medium to differentiate streptococci into several 

 groups : 



Streptococcus pyogenes or erysipelatos, grayish colonies surrounded by a 

 zone of hemolysis. 



Streptococcus viridans, greenish colonies, very slight, if any, hemolysis. 



Streptococcus mucosus, slimy colonies, no hemolysis. 



Streptococci do not form spores and do not produce indol. 



Powers of Resistance. Streptococci are much less resistant to germicidal 

 agents than staphylococci. Pathogenic forms lose their virulence by cultiva- 

 tion on culture media; cultures die out in the course of days or weeks; drying 

 rapidly reduces virulence and kills in the course of weeks; at i2oC. in hot-air 

 sterilizer they are destroyed in J^ hour; in a moist state exposure to 6oC.,for 

 from }4 to i hour kills; boiling is almost instantly destructive. Saprophytic 

 forms are more resistant. 



TOXIN 



Streptococci possess a variable intracellular toxin; attempts to produce an 

 antitoxin have been futile. 



Agglutinins do not appear in the blood of those infected with streptococci. 

 Experimentally, animals can be made to produce agglutinins, but agglutination 

 tests are unsatisfactory in diagnosis and bacteriological classification. The 

 same is true regarding amboceptors and complement fixation tests. 



Antistreptococci sera have not given satisfactory therapeutic results. 

 Bacterial vaccines are of value in combatting infection and increasing resist- 

 ance to streptococci, in selected cases. 



PATHOGENESIS 



Streptococci, like staphylococci, are strikingly variable in virulence; some 

 are non-pathogenic, others but feebly pathogenic and some are extremely viru- 

 lent. Virulence not only varies in different strains of streptococci, but individ- 

 uals show marked variations in pathogenicity at different times. Virulence 

 is increased by passage through animals, especially rabbits and man. It is 

 decreased by cultivation on artificial media and saprophytic existence. Organ- 

 isms isolated from a person whom they killed lose their pathogenic power to 

 a large degree by cultivation on culture media for a long time. If such an at- 

 tenuated culture is passed through several rabbits its original virulence may be 

 restored. 



Streptococci may be associated with disease either as its exciting cause or as 

 secondary invaders, complicating or aggravating a condition that started as a 

 staphylococcus infection, tuberculosis or other infection. 



Streptococcus infections, like staphylococcus infections, may be localized, 

 the organisms confined to a circumscribed portion of the body, or they may be 

 septicemic, the organisms pervading the blood-stream. 



Any portion or tissue may be involved; as a rule, localized streptococcic 

 lesions show a greater area of inflammation and edema in proportion to the 



