240 NATURE OF ANTIBIOTIC ACTION 



hydrolyzate medium j the activity was increased to 6,000 by addition 

 of ^-amino-benzoic acid in dilution of 1:2,500 to i:io,oooj this was 

 also true in presence of glucose in test medium. A similar, although 

 somewhat lower, increase took place with S. aureus; no effect was ob- 

 tained with S. hemolyticus. The addition of a dilute solution of sulfa- 

 pyridine, which in itself had little inhibiting effect, exerted an even 

 greater synergistic action upon penicillin. This effect was exerted not 

 only in vitro but also in vivo (921). 



Various gram-negative bacteria have been found to be susceptible to 

 penicillin in a medium devoid of amino acids j the action of these ap- 

 parently consists in neutralizing the action of penicillin upon these bac- 

 teria (431). Various bacteria are capable of producing penicillin-de- 

 stroying or penicillin-inhibiting substances. Penicillinase is an enzyme j 

 it is produced by E. coli and other bacteria j it is inactivated by heat and 

 at fYL 3.0 and 9.0. Anti-penicillin is not an enzyme j it is produced by 

 B. subtiUs (yiS^) ; it is heat stable. 



The ability of penicillin to destroy the bacteroids in cockroaches was 

 interpreted (95) as indicative of the fact that these bacteroids are not 

 parasitic but rather symbiotic microorganisms. 



Penicillin was also found (409) to be able to inhibit the rate of cell 

 division of fertilized sea urchin eggs when used in concentrations of 

 250 to 2,500 O.U./ml. It inhibits the adsorption of methylene blue on 

 activated charcoal, in concentrations as low as 100 O.U./ml. 



Streftothricin and Streptomycin 



Streptothricin and streptomycin are active against both gram-positive 

 and gram-negative bacteria, although they differ in antibiotic spectra 

 and in toxicity to animals. They are soluble in water but insoluble in 

 alcohol and other organic solvents. Both have an optimum reaction at 

 ^H 8.0, and both are repressed by glucose and by acid salts. Both are 

 stable compounds and are highly resistant to the action of microorgan- 

 isms. However, the two substances can be differentiated in their relation 

 to cysteine. Streptomycin becomes inactivated by the addition of 3 to 5 

 mg. of this compound to 100 pg of the antibiotic, whereas strepto- 

 thricin is not affected by it (179). 



The antibacterial activity of streptomycin can be largely or com- 



