Evaluation of a new E-test method for antimicrobial sensitivity testing of Pseudomonas aeruginosa isolates from cystic fibrosis

BACKGROUND: Sputum bacteriological analysis of cystic fibrosis (CF) patients colonised by Pseudomonas aeruginosa is difficult. The bronchial persistence of these bacteria involves phenotypical modifications and the many antibiotic treatments result in emergence of multiresistant strains. The aim of this study is to evaluate a new fast identification and sensitivity testing method of P. aeruginosa and other pathogenic bacteria in sputum of CF patients. It is based on applying a gradient of antibiotic (E-test strip) onto an agar plate inoculated with the sputum. OBSERVATIONS: 310 sputum, collected from adults and children colonised by P. aeruginosa, were analysed by this new method. This method allowed a direct reading of the minimal concentration of antibiotic that inhibited the totality of Gram-negative strains and the detection of resistant pathogenic bacteria inside the ellipse of inhibition. Results obtained by this new method were compared with the conventional method for identification and antimicrobial sensitivity. CONCLUSION: This new method, studying with CF patient colonised by P. aeruginosa, appears interesting, with a sensibility equal or higher than 89% in detection of the bacteria and their sensitivity to antibiotics. Furthermore it allows a saving of time and simplified results.