JAC Advance Access originally published online on September 6, 2002
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Journal of Antimicrobial Chemotherapy (2002) 50, 517-523
© 2002 The British Society for Antimicrobial Chemotherapy
Clinical significance of inhibition kinetics for Streptococcus pyogenes in response to penicillin

1 Department of Pediatrics, University Hospital Innsbruck, Innsbruck; 2 Institute of Hygiene, University of Innsbruck, Innsbruck; 3 Department of Transplant Surgery, D. Swarovski Research Laboratory, University Hospital Innsbruck, Anichstrasse 35, A-6020 Innsbruck, Austria
Received 14 January 2002; returned 24 May 2002; revised 8 July 2002; accepted 15 July 2002
Objectives: The antibiotic mode of action against clinical isolates of Streptococcus pyogenes and physiological factors involved in modifying the inhibitory response to the antibiotic were investigated.
Methods: We developed high-resolution respirometry for continuous monitoring of bacterial growth and inhibition kinetics. One hundred and ten clinical isolates from 90 paediatric patients were tested, including 48 isolates obtained from 28 patients with eradication failure. Respirometric inhibition curves were monitored at 4 mg/L penicillin G over a short 30 min period, corresponding to the drugs serum half-life.
Results: None of the clinical isolates exhibited penicillin tolerance. Latency in the respirometric response of S. pyogenes to penicillin increased significantly with decreasing strain-specific respirometric growth rate. No difference in inhibition kinetics was found in vitro for isolates from patients with or without bacteriological treatment failure.
Conclusions: In streptococcal pharyngotonsillitis, tolerance is not a relevant concept to explain bacteriological treatment failure. Definitions of tolerance should be reconsidered in the framework of growth-dependent antibiotic susceptibility.
* Present address. Institute of Virology, University of Vienna, Austria
Corresponding author. Tel: +43-512-504-4623; Fax: +43-512-504-4625; E-mail: erich.gnaiger{at}uibk.ac.at