Detection of blaSPM-1 Metallo-β-Lactamase Gene in Imipenem-Resistant Pseudomonas aeruginosa Strains Isolated From Hospitalized Patients in Isfahan Hospitals

Abstract

Background: 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 to some difficulties in treating bacterial infections. The blaSPM-1 is one of the MBL gene families, which induces resistance to the carbapenem class antibiotics; this gene has not been previously assessed in Iran. Objectives: Detection and quantification of blaSPM-1- metallo-β-lactamase gene among resistant Pseudomonas aeruginosa strains (imipenem), isolated from patients in Isfahan hospitals. Patients and Methods: A total of 180 samples were isolated from various nosocomial infections. These isolates were identified as Pseudomonas aeruginosa by using biochemical tests. In order to determine their bacterial drug resistance-pattern the Kirby-Bauer disk diffusion method was utilized. Presence of MBLs in imipenem isolates was detected using the combine disk technique (IMP-EDTA). Similarly, an E-test on Mueller-Hinton agar was used to determine the minimal inhibitory concentration (MIC) of imipenem isolates. The imipenem isolates were then subjected to polymerase chain reaction (PCR) to detect the blaSPM-1 gene. Data were analyzed using the SPSS software (version 16, SPSS Inc., Chicago, IL, USA). Results: In total, 96 isolates of Pseudomonas aeruginosa were collected. Of all isolates, 34 (35.41%) were found to be imipenem-resistant P. aeruginosa. The MIC levels in all imipenem-resistant strains were MIC ≥ 32 μg/mL. Thirteen (38.23%) of the imipenem-resistant P. aeruginosa isolates were MBL positive. None of the isolates carried the blaSPM-1 gene, as indicated by the PCR assay. Conclusions: The rate of imipenem resistance due to MBL has increased dramatically. Early detection and infection-control practices are the best antimicrobial strategy for this organism.