[Growth curves and killing rate of Haemophilus influenzae exposed to amoxicillin, cefaclor and cefotaxime].
The antibacterial activity of beta-lactams against H. influenzae is difficult to evaluate as a result of the osmotic-pressure-dependent formation of filaments and spheroplasts whose viability is still under debate. We compared growth curves obtained by optic density measurements and by UFC/ml counts for H. influenzae in the presence of amoxicillin, cefaclor and cefotaxime in various concentrations. Only the early response to antibiotics, observed during the first six hours of antibiotic-culture contact, was considered. Results showed, for each of the three antibiotics: an increase in optic density with formation of abnormal organisms that correlated poorly with antibiotic concentrations; a stable number of UFC/ml for more than 90 mn, followed by a slow fall reaching at the most 1.5 Log 10 UFC/ml at the sixth hour. We conclude that amoxicillin, cefaclor and cefotaxime in active concentrations rapidly produce the formation of abnormal organisms with an increase in biomass as a result. These abnormal organisms lose their viability slowly, even with concentrations greater than 50 time the MIC. Cefaclor's MIC and MBC are underestimated when results are read only after 24 hours.
D000658:Amoxicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002433:Cefaclor / Q000494:pharmacology; D002439:Cefotaxime / Q000494:pharmacology; D003720:Densitometry; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000254:growth & development; D013997:Time Factors
D000900:Anti-Bacterial Agents; D002433:Cefaclor; D000658:Amoxicillin; D002439:Cefotaxime
Courbes de croissance et vitesse de mort d'Haemophilus influenzae soumis à l'amoxicilline, au céfaclor et à la céfotaxime.