1. Academic Validation
  2. In vitro and in vivo activities of piperacillin-tazobactam and meropenem at different inoculum sizes of ESBL-producing Klebsiella pneumoniae

In vitro and in vivo activities of piperacillin-tazobactam and meropenem at different inoculum sizes of ESBL-producing Klebsiella pneumoniae

  • Clin Microbiol Infect. 2014 Nov;20(11):O831-9. doi: 10.1111/1469-0691.12677.
Y Harada 1 Y Morinaga N Kaku S Nakamura N Uno H Hasegawa K Izumikawa S Kohno K Yanagihara
Affiliations

Affiliation

  • 1 Department of Laboratory Medicine, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan; Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
Abstract

The inoculum effect is a laboratory phenomenon in which the minimal inhibitory concentration (MIC) of an Antibiotic is increased when a large number of organisms are exposed. Due to the emergence of extended-spectrum β-lactamase-producing Klebsiella pneumoniae (ESBL-Kpn) infections, the inoculum effect of ESBL-Kpn on β-lactams was studied in vitro and in vivo using an experimental model of pneumonia. The in vitro inoculum effect of 45 clinical ESBL-Kpn isolates on β-lactams was evaluated at standard (10(5) CFU/mL) and high (10(7) CFU/mL) organism concentrations. The MIC50 of piperacillin-tazobactam, cefotaxime and cefepime was increased eight-fold or more and that of meropenem was increased two-fold. The in vivo inoculum effect was evaluated in an ESBL-Kpn pneumonia mouse model treated with bacteriostatic effect-adjusted doses of piperacillin-tazobactam (1000 mg/kg four times daily, %T>MIC; 32.60%) or meropenem (100 mg/kg twice daily, %T>MIC; 28.65%) at low/standard (10(4) CFU/mouse) and high (10(6) CFU/mouse) inocula. In mice administered a low inoculum, no mice died after treatment with piperacillin-tazobactam or meropenem, whereas all the control mice died. In contrast, in the high inoculum model, all mice in the piperacillin-tazobactam-treated group died, whereas all meropenem-treated mice survived and had a decreased Bacterial load in the lungs and no invasion into the blood. In conclusion, meropenem was more resistant to the inoculum effect of ESBL-Kpn than piperacillin-tazobactam both in vitro and in vivo. In the management of severe pneumonia caused by ESBL-Kpn, carbapenems may be the drugs of choice to achieve a successful outcome.

Keywords

Extended-spectrum β-lactamase; Klebsiella pneumoniae; inoculum effect; meropenem; piperacillin-tazobactam; pneumonia.

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