In vitro postantibiotic effect of biapenem, a new carbapenem antibiotic

Abstract

In vitro postantibiotic effect (PAE) of biapenem (BIPM), a new carbapenem antibiotic, was investigated.
The test organisms were exposed to 4-fold MIC of BIPM, imipenem (IPM), ofloxacin (OFLX) or ceftazidime (CAZ) for 1.5 hours.All the test antibiotics showed PAEs of 2 to 5 hours against Staphylococcus aureus. BIPM and IPM showed long PAEs of 6.2 hours and 7.0 hours respectively, however, OFLX showed short PAE of 1.8 hours against methicillin resistant S. aureus.
Against Escherichia coli or Citrobacter freundii, BIPM and IPM showed short PAEs of 0 to 1.0 hour and 0.5 to 1.3 hours respectively, and CAZ showed negative PAEs of -0.7 to 0 hour, however, OFLX showed PAEs of 2.3 to 3.7 hours.
BIPM as well as IPM showed PAEs of 0.5 to 3.0 hours, and OFLX showed PAEs of 1.0 to 2.3 hours against Pseudomonas aeruginosa.
Morphological changes of E. coli in the duration of PAE were investigated. Exposure to BIPM or IPM at 4 fold MIC for 1.5 hours induced round cell formation, whereas exposure to CAZ induced filamentous cell formation. After antibiotics removal, round cell formation of E. coli by BIPM or IPM was sustained for 2 to 3 hours and slight growth of cell was observed. On the other hand, after CAZ removal, filamentous cell of E. coli returned to rod cell and significant growth of cell was observed.