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Bactericidal effect and regrowth of Streptococcus faecalis exposed to amoxicillin following β-lactamase

par Yourassowsky, Eugène ;Van der Linden, Martial;Lismont, M.J.;Crockaert, F.;Glupczynski, Youri
Référence Chemotherapy, 34, 6, page (462-466)
Publication Publié, 1988

Article révisé par les pairs

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Résumé :

Streptococcus faecalis usually requires high concentrations of penicillin or ampicillin to achieve killing (i.e. a high MBC/MIC ratio). However, most strains show the Eagle or paradoxical effect. We subjected 12 strains of S. faecalis to 0.1, 1, 10 and 100 μg/ml of amoxicillin. Turbidometry studies have shown that 3 h after the inactivation of amoxicillin by penicillinase, there was a longer effect for 1 μg/ml following β-lactamase (12 h 31 min ± 2 h 09 min) than for 10 μg/ml (7 h 0 min ± 1 h 12 min) or 100 μg/ml (5 h 22 min ± 0 h 52 min). After 3 h, the reduction of CFU/ml (inoculum 106 CFU/ml) was -1.8 ± 0.6 for 1 μg/ml, -0.56 ± 0.56 for 10 μg/ml and -0.21 ± 0.20 for 100 μg/ml. The more rapid killing at 3 h was not the only reason for the longer effect following β-lactamase observed with 1 μg/ml. Indeed, the growth curve obtained with an inoculum of 103 CFU/ml was 2 h delayed from the control curve (106 CFU/ml). In conclusion, a paradoxical effect (killing curves and effect following β-lactamase) was observed for all S. faecalis strains included in this series.