Detection of blaSPM-1 metallo-β-lactamase gene in Imipenem-resistant Pseudomonas aeruginosa strains isolated from hospitalized patients in Isfahan hospitals

Pseudomonas aeruginosa is an opportunistic human pathogen which causes serious problems especially in people who have immunodeficiency. Recently, metallo-β-lactamase (MBLs) resistance in this bacterium has led some difficulties in treating bacterial infections. MBL gene family, including blaSPM-1 caused resistance to beta-lactam antibiotics especially carbapenem (eg, imipenem) and have been reported with high prevalence worldwide. The aim of this study is detection of metallo-β-lactamase gene blaSPM-1 in Imipenem-resistant Pseudomonas aeruginosa strains isolated from hospitalized patients in Isfahan hospitals. In this study, 252 samples were isolated from various nosocomial infections. These isolates were identified as Pseudomonas aeruginosa by using biochemical tests. Disk diffusion method (Kirby-Bauer) was used to determine the bacterial drug resistance pattern. All imipenem-resistant isolates were screened for the presence of MBLs by using the Combine disk (IMP-EDTA). The minimal inhibitory concentration (MIC) of imipenem was determined by E-test on Mueller-Hinton agar. To detect blaSPM-1 gene, the isolates were subjected to polymerase chain reaction (PCR). In total, 106 isolates of Pseudomonas aeruginosa were collected. Of all isolates, 62 (58.5 %) were found to be imipenem-resistant Pseudomonas aeruginosa. MIC levels in all strains of imipenem-resistant were MIC≥32μg/ml. Twenty-six (48 %) of imipenem-resistant Pseudomonas aeruginosa isolates were MBL positive. None of the isolates carried blaSPM-1 gene by PCR assay. Discussion and Results of this study demonstrate that the rate of imipenem resistance due to MBL is increased dramatically. Early detection and infection-control practices are the best antimicrobial strategies for this organism. None of MBL-producing isolates in this study carry blaSPM-1 gene; therefore another gene in MBLs family should be investigated.