Evaluation of PPI-0903M (T91825), a novel cephalosporin: bactericidal activity, effects of modifying in vitro testing parameters and optimization of disc diffusion tests.
OBJECTIVE
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 microg).


RESULTS
PPI-0903MMBC/MIC ratios were < or = 4 in 90% of strains tested. Kill-curve studies showed >99.9% killing at concentrations < or = 4x 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 microg disc content would be recommended for optimal correlation of MIC breakpoints of < or = 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.
Jones
Ronald N
RN
JMI Laboratories, Inc., 345 Beaver Kreek Centre, Suite A, North Liberty, IA 52317, USA.
Fritsche
Thomas R
TR
Ge
Yigong
Y
Kaniga
Koné
K
Sader
Helio S
HS
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests / Q000379:methods*; D044967:Serum; D000097583:Ceftaroline
D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D003470:Culture Media; D000097583:Ceftaroline