In vitro evaluation of biapenem, a new carbapenem antibiotic

Abstract

The in vitro antibacterial activity of biapenem (BIPM), a new carbapenem antibiotic, was compared with those of imipenem (IPM) and ceftazidime (CAZ).
BIPM had broad-spectrum activity against gram -positive and gram -negative aerobes. Antibacterial activity of BIPM against gram-positive bacteria of clinical isolates was much superior to those of the cephalosporins tested but inferior to that of IPM. However, against methicillin resistant Staphylococcus aureus characterized by resistance to carbapenems, such as IPM or BIPM, in combination with cefotiam and cefuzonam, showed strong synergistic activity in vitro. The MIC₉₀ of BIPM against 359 gram -negative clinically isolated strains ranged from 0.2 to 3.13 μg/ml, and its activity was the most potent among the antibiotics tested. Especially, BIPM showed excellent activity against glucose non-fermentric bacteria, such as Pseudomonas aeruginosa or A cinetobacter calcoaceticus. Moreover, this compound had the most potent activity against various β lactamase producing strains except Xanthomonas maltophilia. Besides, there was no change in a susceptibility of this compound against mutants of P. aeruginosa PAO 1 selected by CAZ or ofloxacin. The bactericidal activity of BIPM was not affected by any growth phase of P. aeruginosa. However, in a case of CAZ there is a tendency for the potency to become reduced at early stationary growth phase in comparison with at log phase.
The results obtained in morphological observation by the scanning electron microscope-that is, the formation of spherical cells-reflected the potent antipseudomonal activity of BIPM. Besides, we recognized its activity even against slow growing bacteria under low temperature and low nutrient conditions.