[Evaluation of a E-test method to detect bactericidy of beta lactam-aminoglycoside associations against Pseudomonas aeruginosa isolates from cystic fibrosis]. / Mise au point d'une méthode de mesure d'associations d'antibiotiques bactéricides par superposition de bandelettes E-test((R)) appliquée aux souches de Pseudomonas aeruginosa isolées au cours de la mucoviscidose.

BACKGROUND: Pulmonary infectious exacerbations with Pseudomonas aeruginosa are the major problem for patients with cystic fibrosis. Emergence of multi-resistant mucoid strains leads to complicate the choice of antibiotherapy. Therefore, synergic and bactericidal treatment must be used. Then, it is interesting to estimate the bactericidal activity of antibiotics associations in order to optimise the treatment. The aim of this work is to describe a new method of bactericidal antibiotics combinations by superimposing 2 E-test strips and to compare results with those obtained with a broth bactericidal method chosen as reference method. OBSERVATIONS: Twenty strains of P. aeruginosa (13 mucoïd and 7 non mucoïd) were selected from expectorants of cystic fibrosis children. Four antibiotics combinations were tested (ceftazidime/tobramycine, cefepime/tobramycine, ceftazidime/amikacine, cefepime/amikacine). Two antibiotics combinations by superimposing E-test strips techniques were used: maximal concentration on maximal concentration (C(max)/C(max)) and minimal inhibitory concentration on minimal inhibitory concentration (MIC/MIC). The comparison of results between killing curves and superposition of E-test strips (C(max)/C(max)) show 88% agreements, 4% major discrepancies specially with mucoid strains and 8% minor discrepancies. The Cmax/Cmax method seems to give better results than MIC/MIC method. CONCLUSION: The superposition of E-test strips method is an attractive method: it is rapid, easy to use and well correlated to broth bactericidal method.