Phenotypic detection of metallo--lactamase producing Pseudomonas aeruginosa isolated from Urmia hospitals

Abstract

Detection of metallo-beta-lactamase producing Pseudomonas aeruginosa is crucial for the optimal treatment of patients; however there are limited studies on metallo-beta-lactamase producing P. aeruginosa isolates from West Azarbayejan, Iran. This study was designed to detect the metallo-beta-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 Muller-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-beta-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 = 8 mg/L). The rates of resistance to different antibiotics were much higher in Imipenem resistant isolates. Detection of metallo-beta-lactamase producing isolates among Imipenem non-susceptible isolates of P. aeruginosa revealed that seven isolates (33.3%) were metallo-beta-lactamase positive. Metallo-beta-lactamase positive isolates showed high resistances to all tested antibiotics. This result suggests that metallo-beta-lactamase producing isolates in hospitals may cause serious infections which can lead to failure in patient's antibiotic therapy.