Kinetics and Mechanisms of Action of Trimethoprim and Sulfonamides, Alone or in Combination, upon <i>Escherichia coli</i> (Part 1 of 2)

Abstract

The steady state growth of E. coli cultures is inhibited by either sulfonamide (SA) or trimethoprim (TMP) with a rate constant, k_app1The new steady state is obtained immediately after the addition of TMP whereas a lag phase of about 5 generations is observed for SA. In TMP-treated cultures the slope of the logarithmic growth curve decreases after an initial inhibited growth and a second steady state is established, k_app2 The appearance of the second ‘phase’is dependent on the number of germs but not on the number of generations. Using prewashed cell cultures it was shown that the presence of the first phase is due to an antagonist excreted into the culture medium. The inhibitory effect of TMP is also partly antagonized by thymidine. The inhibitory effect of TMP is about 5 times larger than the effect of sulfamethoxazole (Gantanol®, GT) as evaluated from the plot of 1/k₀––k_app vs. 1/C or C k₀/k₀––k_app vs. C respectively. In cultures where the growth was totally stopped by high concentration of SA no inhibitory effect of TMP is observable. The inhibitory effect of TMP is found to be reversible if the drug containing culture is diluted. The antibacterial effects of TMP alone were seen to be considerably more complex than those of sulfonamides despite their presumable similar sites of action. Even at very high concentrations SA act only bacteriostatically, whereas TMP alone can cause bactericidal effects if a certain threshold of concentration (≥1 µmol/l) is passed. (A decrease in numbers of cells of about 90% can be obtained within 8 h.) Combinations of TMP and SA at concentrations where both drugs are acting merely bacteriostatically lead to effects considerably greater than would be expected from simple additivity. This study of generation rate constants in inhibited cultures indicates that the claim for synergism and bactericidal effect as usually defined is indeed valid for this combination. It seems possible that both the effects in inhibited cultures by TMP alone and its combination with sulfonamides might be explained if one were to assume that TMP has an additional mode of action separate from its known inhibition of dihydrofolate reductase.

Bacterial Growth Kinetics of <i>Escherichia coli</i> and Mycobacteria in the Presence of Brodimoprim and Metioprim Alone and in Combination with Sulfamerazine and Dapsone (VI)

“…This is consistent with the proposed site of action [Seydel et al, 1972], At low concentrations the antibacterial effect is of bacteriostatic nature for the TMP derivatives as well as for SA and DDS. From dose-response curves the iso values are determined using an iteration programme [Schaper.…”

“…Bacterial growth kinetic techniques have been shown to be an especially suit able model for the quantification of drug action and to differentiate between antag onistic, additive or synergistic effects of drug combinations [Seydel et al, 1972[Seydel et al, , 1973Wempe, 1977, 1978). In previous papers we have reported on such studies to quantify the synergistic action of trimethoprim (TMP) in the presence of various sulfonamides (SA).…”

Microbial Kinetics and Dependencies of Individual and Combined Antibiotic Inhibitors of Protein Biosynthesis

“…This has been clearly shown in the effect on the kinetics of microbial generation for combinations of trimethoprim and sulfonamides (6,15,28).…”

Investigations on Plasma Levels of Sulfamethoxazole in Man after Single and Chronic Oral Administration Alone and in Combination with Trimethoprim

“…has been studied extensively [1,9,15]. The clinical usefulness of this chemo therapeutic combination is well established [6].…”