Journal Article

Evaluation of PPI-0903M (T91825), a novel cephalosporin: bactericidal activity, effects of modifying <i>in vitro</i> testing parameters and optimization of disc diffusion tests

Ronald N. Jones, Thomas R. Fritsche, Yigong Ge, Koné Kaniga and Helio S. Sader

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 56, issue 6, pages 1047-1052
Published in print December 2005 | ISSN: 0305-7453
Published online October 2005 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dki362
Evaluation of PPI-0903M (T91825), a novel cephalosporin: bactericidal activity, effects of modifying in vitro testing parameters and optimization of disc diffusion tests

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Objectives: To evaluate bactericidal activity of PPI-0903M and in vitro testing parameters for this compound.

Methods: A total of 110 strains were tested to determine MIC and MBC values of PPI-0903M. MIC values were determined by reference broth microdilution whereas MBC was assessed by plating the broth from the MIC well and from those wells above the MIC for each organism onto appropriate drug-free growth media. Seventeen strains were tested by the kill-curve methodology to again evaluate the bactericidal activity of PPI-0903M. Broth microdilution results for 15 strains (in triplicate) were compared with the standard, reference method after modifying several testing parameters. Optimal disc content was assessed by testing seven reference strains with five PPI-0903M disc concentrations (5, 10, 30, 50 and 100 µg).

Results: PPI-0903MMBC/MIC ratios were ≤4 in 90% of strains tested. Kill-curve studies showed >99.9% killing at concentrations ≤4× MIC within 8 to 24 h against staphylococci and Enterobacteriaceae tested. PPI-0903M MIC results were rarely influenced by the test or medium changes evaluated [high inoculum, low calcium or reduced pH (5.0)]. Human serum had no effect on in vitro antimicrobial activity of PPI-0903M. The 10 µg disc content would be recommended for optimal correlation of MIC breakpoints of ≤1–4 mg/L.

Conclusions: PPI-0903M was generally bactericidal against tested species, and the MIC results were stable across numerous susceptibility test condition changes.

Keywords: PPI-0903M; anti-MRSA cephalosporins; MRSA

Journal Article.  1943 words.  Illustrated.

Subjects: Medical Oncology ; Critical Care

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