STUDIES ON SYNERGISTIC ACTION AGAINST PENICILLIN AND CEPHALOSPORIN RESISTANT BACTERIA

Section I: Laboratory Studies

Abstract

Studies on the synergistic action of derivatives of penicillin or cephalosporin were investigated in vitro, employing four strains of gram negative rod bacteria which were isolated from urinary tract infections and resistant against cephaloridine (CER) and ampicillin (AB-PC). The strains tested were Citrobacter 205, Klebsiella 343, E. coli K-12/R 743 (received R-factor carrying penicillin resistant marker from. Rettgerella 743) and Pseudomonas 1050. The patterns of these strains were different from each other. The combinations of drugs in the studies presented were CER-methicillin (DMP-PC) and AB-PC-DMP-PC. The inhibitory effect of the combination on bacterial growth was investigated by turbidmetric assay of growth in broth, plate dilution test and disc test. Enzymological studies were performed employing DMP-PC as an inhibitor of hydrolytic β-lactamase action. Kinetic studies were done also. Synergistic action of CER and DMP-PC was well demonstrated in Citrobacter 205, which was moderately resistant against CER and showed weak cephalosporinase activity. Klebsiella 343 was highly resistant against CER and AB-PC and showed high cephalosporinase activity. On this strain the synergistic action of CER and DMP-PC was clearly demonstrated. However, the growth inhibitory effect of AB-PC and DMP-PC on the strain was only additive. It might be explained by lower affinity of CER to the enzyme and higher affinity of penicillin from the results of kinetic analysis of the enzyme produced by Klebsiella. 343. On E. coli K-12/R 743, no synergistic action was observed even at a high concentration (4mg/ml) of each drug. On Pseudomonas 1050, inspite of very low activity of β-lactamase, synergistic action was demonstrated in the combination of CER and DMP-PC. Generally, synergistic action was observed. more clearly in the combination of CER and DMP-PC than in that of AB-PC and DMP-PC, The mechanism of synergistic action has been thought to be chiefly due to inhibitory effect of DMP-PC on β-lactamase action, but as in the case of Pseudomonas 1050, the above explanation might be incomplete. Further investigations are necessary