Behaviour of some derivatives of 7-aminocephalosporanic acid and 6-aminopenicillanic acidas substrates, inhibitors and inducers of penicillinases

ANTIBACTERIAL ACTIVITY OF SOME DERIVATIVES OF 7-AMINOCEPHALOSPORANIC ACID AGAINST STAPHYLOCOCCUS AUREUS AND SYNERGISM BETWEEN THESE AND OTHER ANTIBIOTICS

The N-phenylacetyl derivative of 7-aminocephalosporanic acid (cephaloram) had roughly the same activity as benzylpenicillin against a number of Gram-positive organisms and about one-eighth of the activity of benzylpenicillin against penicillinsensitive strains of Staphylococcus aureus. This derivative and the N-alpha-phenoxypropionyl derivative of 7-aminocephalosporanic acid were 4 to 8 and 4 to 16 times as active as methicillin against penicillinase- and nonpenicillinase-producing staphylococcal strains, respectively. Neither the presence of horse serum nor changes in inoculum size appreciably affected the activities of any of the derivatives of 7-aminocephalosporanic acid which were tested. After forty-eight subcultures in the presence of antibiotic the increase in minimum inhibitory concentration against the staphylococcus was about four-times as great for cephaloram as for cephalosporin C. The resistant penicillinase-producing strains remained stable after six subcultures in antibiotic-free medium, and all the strains retained coagulase activity. Some degree of cross-resistance was found between the derivatives of 7-aminocephalosporanic acid and those of 6-aminopenicillanic acid. Synergism was observed in vitro between certain derivatives of 7-aminocephalosporanic acid and 6-aminopenicillanic acid when they were tested together or with fusidic acid or cephalosporin P(1) against a weak penicillinase-producing strain of Staphylococcus aureus. Cephalosporin C and cephalosporin C (pyridine), each in combination with benzylpenicillin, showed a significant degree of synergism in protection experiments in mice infected with a strong penicillinase-producing strain of Staphylococcus aureus.

INDUCTION OF STAPHYLOCOCCAL PENICILLINASE BY BENZYLPENICILLIN: EFFECT OF pH, CONCENTRATION OF FERROUS ION AND INDUCER, AND DURATION OF EXPOSURE OF CELLS TO INDUCER

Leitner, Felix (Michael Reese Hospital and Medical Center, Chicago, Ill.), Helen M. Sweeney, T. F. Martin, and Sidney Cohen . Induction of staphylococcal penicillinase by benzylpenicillin: effect of pH, concentration of ferrous ion and inducer, and duration of exposure of cells to inducer. J. Bacteriol. 86: 717–727. 1963.—The kinetics of induction of penicillinase by benzylpenicillin in exponentially multiplying Staphylococcus aureus strain 55-C-1 were shown to vary with the pH. At pH 7.3 in the absence of free inducer, the rate of increase of penicillinase activity rapidly declined and came to a halt. At pH 5.4 to 5.5 and in the presence of optimal concentrations of Fe ++ , the penicillinase activity of the induced culture increased linearly with time for 2.5 or more generations, but the rate of increase usually declined eventually. Evidence was advanced to support the concept that the acidic pH and optimal Fe ++ concentration maintain the induced formation of enzyme. The induced increase in penicillinase activity appeared 3 to 4 min after the addition of benzylpenicillin. The degree of induction of penicillinase varied with the duration of exposure of the staphylococci to the inducer and with the concentration of inducer. Maximal induction under our conditions was attained by exposure for 15 min to benzyl-penicillin at an initial concentration between 0.6 and 2 units/ml.