Abstract

Detection of metallo-β-lactamase producing Pseudomonas aeruginosa is crucial for the optimal treatment of patients; however there are limited studies on metallo-β-lactamase producing P. aeruginosa isolates from West Azarbayejan, Iran. This study was designed to detect the metallo-β-lactamase in P. aeruginosa isolates. One hundred isolates were collected from clinical specimens submitted to hospital diagnostic laboratories in Urmia/Iran from July to September 2010. The susceptibilities of the isolates to different classes of antibiotics were tested using Müller-Hinton agar disk diffusion method. All isolates of P. aeruginosa were subjected to determination of minimum inhibitory concentrations )MICs) against Imipenem. Imipenem non-susceptible isolates were investigated for metallo-β-lactamase production by the combined disk method. The rates of resistances to antibiotics, as were determined, is as follows: kanamycin (91%), Tobramycin (34%), Ciprofloxacin (16%), Colistin (68%), Ticarcillin (46%), Amikacin (16%), Norfloxacin (23%), gentamicin (33%), Ceftazidime (62%), Ceftizoxime (69%), and Cefepime  (39%). Seventy nine isolates (79%) were sensitive (MIC ≤ 4 mg/L) and 21 isolate (21%) were resistant to Imipenem (MIC ≥ 8 mg/L). The rates of resistance to different antibiotics were much higher in Imipenem resistant isolates. Detection of metallo-β-lactamase producing isolates among Imipenem non-susceptible isolates of P. aeruginosa revealed that seven isolates (33.3%) were metallo-β-lactamase positive. Metallo-β-lactamase positive isolates showed high resistances to all tested antibiotics. This result suggests that metallo-β-lactamase producing isolates in hospitals may cause serious infections which can lead to failure in patient’s antibiotic therapy.

Key words: Pseudomonas aeruginosa, metallo-β-lactamase and Imipenem.