In VitroStudies Concerning the Action of Penicillin on the Viridans Streptococci, Including Observations on the So-called Synergistic Effect of Sulfonamide Drugs

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Abstract
From studies of the in vitro action of penicillin on various strains of viridans streptococci, the following observations have been made:[long dash]Concs. of penicillin above the minimal conc. necessary for bacteriostasis have a bactericidal action. For any given strain there is a critical conc. of penicillin beyond which further increases in conc. have no increased bactericidal activity. Strains of viridans streptococci differ not only in regard to the minimal conc. of penicillin necessary for bacteriostasis but also in regard to the rate at which they are killed in the presence of an excess of penicillin. There is need for further studies concerning the possible correlation of these 2 variables. Within wide limits, variations in the number of exposed organisms do not appreciably alter the rate of bactericidal action of penicillin. Sulfonamide drugs seem to have the following effect on the in vitro action of penicillin: (a) The minimal effective conc. of penicillin is reduced for many strains of viridans streptococci, (b) In the presence of penicillin in amts. above the minimal effective conc., sulfonamides do not appreciably alter the bactericidal action of the penicillin.