Phenotypic Detection of Metallo-beta-lactamase Producing Pseudomonas aeruginosa Strains Isolated from Burned Patients

Background and Objective: Metallo-beta-lactamases (MBLS) mediated resistance is an emerging threat in hospital isolates of Pseudomonas aeruginosa. There is not enough information from Iran regarding the prevalence and the screening methods for such enzymes. The present study was undertaken to detect MBLS in strains of P. aeruginosa isolated from burned patient using phenotypic method. Materials and Methods: For this purpose, 128 consecutive P. aeruginosa isolates obtained from hospitalized patients were subjected to susceptibility testing to antipseudomonal drugs by disc diffusion and minimal inhibitory concentration (MIC) for ceftazidime was determined. The production of MBL was detected by the zone size enhancement with EDTA impregnated ceftazidime disc. Results: It was found out that 94 (73.44%) of the isolates were resistant to ceftazidime. These isolates screened as ESBLs producing strains and introduced for detection of MBL production. Out of the 94 P. aeruginosa that were resistant to ceftazidime, 50 (53.2%) isolates were MBL positive. This result indicated that 39.06% of all isolates were MBL positive. Conclusion: MBL-mediated ceftazidime resistance in P. aeruginosa is a cause for concern in the therapy of critically ill patients. The MBL producing P. aeruginosa isolates were more resistant to various antimicrobial agents. This result suggests that MBL producing isolates in hospitals may cause serious infections that illustrated when these strains were responsible for a nosocomial outbreak.