Phenotypic screening of extended-spectrum ß-lactamase and metallo-ß-lactamase in multidrug-resistant Pseudomonas aeruginosa from infected burns.

Pseudomonas aeruginosa is an important opportunistic pathogen causing nosocomial infections, especially in immunocompromised patients such as burn patients. Pseudomonas aeruginosa is potentially resistant to different broad-spectrum antibiotics due to its ability to produce extended-spectrum β-lactamase (ESBL) and metallo-β-lactamase (MBL). In the present 6 month study, 220 strains of multidrug-resistant (MDR) Pseudomonas aeruginosa were isolated from male and female burn patients who had been hospitalized for at least one week in Motahari Hospital in Tehran. These strains were screened by the disc diffusion and double disc methods to determine the capacity of producing ESBL and MBL. Of all strains, 18% were ESBL-positive, resulting in a significant inhibition zone (≥5 mm) with cefotaxime and ceftazidime plus clavulanic acid discs when compared to the plain cefotaxime or ceftazidime discs. 38% of the strains were MBL-positive, showing at least 7 mm difference between the inhibition zone around the imipenem discs alone in comparison with imipenem plus EDTA discs, and at least 5 mm difference between the inhibition zone around imipenem plus EDTA discs and EDTA discs alone. In the light of our results, the rapidly spreading resistance among bacterial populations due to the extensive use of antibiotics is a matter of concern for the optimal treatment of patients, particularly in burn wards, and the determination of ESBL and MBL production of MDR Pseudomonas aeruginosa strains is essential.