Growth curve patterns of Escherichia coli, Serratia marcescens, and Proteus vulgaris submitted to different tigemonam concentrations.

Five strains of Escherichia coli, Serratia marcescens, and Proteus vulgaris were exposed to a new monobactam, tigemonam, in comparison with aztreonam. The study, evaluated by kinetic turbidimetry, has shown that tigemonam exerts a prelytic increase in optical density (OD) similar to that of other beta-lactam antibiotics. The maximal value of the prelytic increase in OD was similar for the two study antibiotics at concentrations of 1, 2, 4, and 8 times the minimum inhibitory concentration, corresponding with filament formation. The OD values varied according to the bacterial species. Bactericidal activity was observed for the three species evaluated. At 6 hours, the killing rate was not dose-related. In conclusion, tigemonam and aztreonam induced first filament formation followed after a few hours by bactericidal activity.