Temocillin breakpoints in pyelonephritis: evaluation in a murine model due to ESBL-producing Escherichia coli clinical isolates Ke ´ vin Alexandre 1,2 *, Anaı ¨s Soares 1,3 ,Franc¸oise Chau 4 , Bruno Fantin 4 , Franc¸oisCaron 1,2 and Manuel Etienne 1,2 1 EA 2656 (GRAM 2.0), IRIB, Normandie Univ, Unirouen, Rouen, France; 2 Infectious Diseases Department, Rouen University Hospital, Rouen, France; 3 Microbiology Department, Rouen University Hospital, Rouen, France; 4 INSERM, IAME, UMR 1137, F-75018 Paris, France *Corresponding author. Tel: !332-32-88-06-74; Fax: !332-32-88-82-75; E-mail: kevin.alexandre@chu-rouen.fr orcid.org/0000-0001-7773-5695 Received 4 September 2018; returned 13 October 2018; revised 14 December 2018; accepted 18 December 2018 Background: Due to a spectrum restricted to Enterobacteriaceae and stability against ESBL and AmpC enzymes, temocillin is of major interest for the treatment of pyelonephritis. But there are still uncertainties about the opti- mal regimen and clinical breakpoints. Objectives: To study in a murine model of pyelonephritis the activity of temocillin against Escherichia coli isolates with different MICs in order to evaluate clinical breakpoints. Methods: Four clinical uropathogenic E. coli isolates with temocillin MICs of 8 mg/L (Ec8), 16 mg/L (Ec16), 32 mg/L (Ec32) and 64 mg/L (Ec64) were evaluated. Antibiotic 24 h T .MIC achieved in humans was reproduced in mice with either intravenous temocillin (2g q12h or 2g q8h) or intravenous imipenem (1g q8h). Efficacy was assessed by bacterial count in kidneys. Results: Compared with controls, temocillin at 2g q12h was highly efficient against Ec8 (#3.32 log 10 cfu/g and negative cultures in 93% of mice; P , 0.001); imipenem gave similar results. Temocillin at 2 g q12h also induced high reduction of bacterial count against Ec16 (#2.92 log 10 cfu/g; P , 0.001), albeit cultures were negative in only 48% of mice. In contrast, no significant effect was observed in mice infected by Ec32 (#0.01 log 10 cfu/g; P " 0.981) or Ec64 (#0.55 log 10 cfu/g; P " 0.523). Even temocillin at 2g q8h failed to control Ec32 infection (#1.55 log 10 cfu/g; P " 0.197). Conclusions: This model suggests a clinical breakpoint up to 16 mg/L for non-severe pyelonephritis treated with temocillin at 2 g q12h, a value consistent with the few previous available data. Introduction Urinary tract infections (UTIs) are the most common human infec- tions due to ESBL-producing Escherichia coli. Temocillin has emerged as an attractive carbapenem-sparing option because of a spectrum mainly restricted to Enterobacteriaceae, a stability against numerous b-lactamases, including ESBL and AmpC enzymes, and minimal risk of Clostridium difficile infection. 1 Debate is, however, still ongoing about the optimal temocillin therapeutic schedule. Current recommended regimens are 2 g q12h or 2g q8h depending on infection severity and strain susceptibility. 1,2 As a consequence, there is still no international consensus regarding temocillin breakpoints, with three different values for susceptible isolates, i.e. MIC 8, 16 and 32 mg/L, depending on the country. 3–5 Two previous animal studies have suggested that a humanized temocillin regimen of 2 g q12h retains activity against E. coli strains with MICs up to 16 mg/L. 6,7 Both studies used genetically modified bacteria. One study used a unique isolate with a temocillin MIC of 8 mg/L, the results being derived from pharmacokinetic calcula- tions. The other study was not conducted in UTI, hence antibiotic concentrations at the site of infection might differ notably. Therefore, we aimed to further study in a murine model of pyelo- nephritis the in vivo activity of temocillin against different ESBL- producing E. coli clinical isolates, in order to contribute to better definition of clinical breakpoints for systemic UTI. Materials and methods Bacterial strains Four clinical uropathogenic E. coli isolates belonging to phylogroup B2 (i.e. the most urovirulent phylogroup) 8 were selected. All produced the most common ESBL currently encountered (i.e. CTX-M-15) 9 with a minimal fitness cost estimated by a maximum growth rate (MGR) 1.4 h #1 (calcu- lated as previously described). 10 Their temocillin MICs (determined by the V C The Author(s) 2019. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please email: journals.permissions@oup.com. 1323 J Antimicrob Chemother 2019; 74: 1323–1326 doi:10.1093/jac/dky569 Advance Access publication 25 January 2019 Downloaded from https://academic.oup.com/jac/article/74/5/1323/5301655 by guest on 25 January 2023