JAC Advance Access originally published online on September 12, 2003
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Journal of Antimicrobial Chemotherapy (2003) 52, 610-615
© 2003 The British Society for Antimicrobial Chemotherapy
Intracellular accumulation and activity of ampicillin used as free drug and as its phthalimidomethyl or pivaloyloxymethyl ester (pivampicillin) against Listeria monocytogenes in J774 macrophages
1 Unité de Pharmacologie Cellulaire et Moléculaire, UCL 73–70, avenue E. Mounier 73, B-1200 Brussels; 2 Unité de Chimie Pharmaceutique et de Radiopharmacie, Université Catholique de Louvain, B-1200 Brussels, Belgium
Received 1 May 2003; returned 16 July 2003; revised 23 July 2003; accepted 28 July 2003
Aims: To determine the intracellular accumulation in a macrophage cell line of ampicillin and ampicillin esters, and to measure their activity against intracellular Listeria monocytogenes.
Methods: Quantitative evaluation of the activity of ampicillin, phthalimidomethylampicillin (PIMA) or pivaloyloxymethylampicillin (PIVA) against intracellular L. monocytogenes, and direct measurement of cellular ampicillin concentration in J774 macrophages.
Results: Ampicillin, PIMA and PIVA caused a 0.5 log decrease in cell-associated cfu within 5 h when used at an extracellular concentration of 3.6 µM [10 x MIC of ampicillin (1.25 mg/L); 1.83 mg/L for PIMA and 1.67 mg/L for PIVA]. Addition of ß-lactamase in the extracellular milieu abolished the activity of ampicillin and of PIMA but not that of PIVA. At low extracellular concentrations [0.5 x MIC ampicillin (62.5 µg/L); equimolar concentrations for PIMA (91.5 µg/L) and PIVA (83.5 µg/L)], ampicillin and PIMA lost all activity (compared with controls), but PIVA remained as active as at the higher concentration. Incubation of cells with PIVA at the low concentration (83.5 µg/L) for 20 h caused a 2 log reduction of cfu if the medium was changed every 5 h (to compensate for the degradation of extracellular PIVA). Incubation of cells with PIVA allowed for a marked (four- to 25-fold) cell accumulation of ampicillin, whereas no ampicillin accumulation was seen for cells incubated with ampicillin or with PIMA.
Conclusions: This is the first demonstration that PIVA (a prodrug of ampicillin) can be used to promote ampicillin cellular accumulation and, thereby to increase ampicillin intracellular activity. PIVA could be useful for control of the intracellular multiplication of L. monocytogenes.
Keywords: prodrugs, ß-lactams, ß-lactamases, infections
* Corresponding author. Tel: +32-2-7647376; Fax: +32-2-7647373; E-mail: hugues.chanteux{at}facm.ucl.ac.be
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