Summary
The responses of bacteria exposed to amoxycillin and ampicillin were studied at continuously decreasing levels with half-life values similar to those which could occur in vivo. ForEscherichia coli, the kill-rates were higher with amoxycillin than with ampicillin. The bactericidal response was exponential. With an antibiotic half-life of one hour, the amoxycillin first order inactivation rate was 3.544 h−1 and the viable cell half-life was 0.196 h; the respective values for ampicillin were 2.341 h−1 and 0.296 h. With an antibiotic half-life of five hours, the inactivation rate was 0.704 h−1 corresponding to a viable cell half-life of 0.985 h for amoxycillin compared to 0.358 h−1 and 1.937 h respectively for ampicillin. Comparison of viable counts and photometric monitoring showed that the former is the preferable method for recording the bacterial response to these β-lactam antibiotics. During the phase of exponential kill, a plateau occurred in the optical density values. This was due in part to an increased biomass per cell. During the recovery phase, the number of viable cells started to increase several hours sooner than did the rise in optical density. ForStaphylococcus aureus, the rates of kill were similar with both agents. Amoxycillin had a long bacteriostatic phase which was not seen with ampicillin. This led to a longer lasting antibacterial effect and reduction to a lower total count with amoxycillin. With staphylococci, the viable counts and the photometric responses were parallel.
Zusammenfassung
Der antibakterielle Effekt von Amoxicillin und Ampicillin in kontinuierlich abfallenden Konzentrationen, deren Halbwertzeiten In-vivo-Bedingungen entsprechen, wurde untersucht. Die Abtötungsraten vonEscherichia coli waren größer mit Amoxicillin als mit Ampicillin und verliefen exponentiell. Bei einer Halbwertzeit von einer Stunde betrug die Amoxicillin-Inaktivierungsrate erster Ordnung 3,544 h−1 und die Halbwertzeit der Lebendzellzahl war 0,196 h; die entsprechenden Werte betrugen für Ampicillin 2,341 h−1 bzw. 0,296 h. Bei einer Antibiotika-Halbwertzeit von fünf Stunden belief sich die Inaktivierungsrate auf 0,704 h−1 mit einer entsprechenden Halbwertzeit der Lebendzellzahlen von 0,985 h für Amoxicillin im Vergleich zu 0,358 h−1 bzw. 1,937 h für Ampicillin. Ein Vergleich der Lebendzellzahl-Bestimmung mit der photometrischen Messung ergibt, daß die erstere Methode zur Erfassung des Effekts von β-Laktam-Antibiotika auf Bakterien besser geeignet ist. Während der exponentiellen Abtötungsphase tritt ein Plateau in den Dichtemessungen auf. Dieser Effekt ist teilweise auf eine Zunahme der zellulären Biomassen zurückzuführen. Während der Erholungsphase nehmen die Lebendzellzahlen einige Stunden früher zu als der Wiederanstieg der optischen Dichte. GegenüberStaphylococcus aureus waren die Abtötungsraten beider Substanzen vergleichbar. Amoxicillin wies eine lange bakteriostatische Phase auf, welche mit Ampicillin nicht beobachtet werden konnte. Dies führte zu einem länger anhaltenden antibakteriellen Effekt und einer größeren Reduktion der Gesamtzellzahl mit Amoxicillin. Mit Staphylokokken verliefen die Lebendzellzahl-Bestimmungen und die photometrischen Messungen parallel.
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Bergan, T., Carlsen, I.B. Bacterial kill rates of amoxycillin and ampicillin at exponentially diminishing concentrations simulating in vivo conditions. Infection 8 (Suppl 1), S103–S108 (1980). https://doi.org/10.1007/BF01644943
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DOI: https://doi.org/10.1007/BF01644943