Investigation of blaIMP-1, blaVIM-1 and blaSPM-1 MBL Genes among Clinical Strains of Pseudomonas aeruginosa Isolated from Imam Khomeini Hospital, Tehran, Iran

Class B beta-lactamases, termed metallo-beta-lactamases (MBLs) such as VIM, IMP and SPM are an increasingly serious clinical problems. They have a very broad substrate profile that includes penicillins, expanded spectrum cephalosporins, and carbapenems, except for monobactames such as aztreonam. MBLs producing Pseudomonas aeruginosa isolates have been responsible for several nosocomial outbreaks. In this study we determined prevalence of blaIMP-1, blaVIM-1 and blaSPM-1 MBL genes among imipenem resistant P. aeruginosa isolated from Imam Khomeini hospital (Tehran, Iran). A total of 243 P. aeruginosa isolates were collected from different clinical samples from Imam Khomeini hospital. After determination of Minimum Inhibitory Concentration (MIC) to imipenem, isolates with MIC≥4 µg/ml were screened for MBLs producing strains by DDST using imipenem-EDTA discs. PCR assay for detection of blaIMP-1, blaVIM-1 and blaSPM-1 MBL genes was performed by specific primer. Among all studied isolates, 28 isolates with MIC≥4 µg/ml to imipenem were selected to DDST with EDTA and PCR assay. Results of this study showed that 22 of these 28 isolates were positive by DDST and 15 isolates harbored blaVIM-1 gene. All these strains were susceptible to colistin and polimixin B. No other MBL studied genes were observed. Our data showed that blaVIM-1 MBL gene is the most frequent gene among clinical P. aeruginosa isolates in this research. According to importance of MBL producing isolates in prolonged nosocomial outbreaks it is necessary to rapid detection and concern seriously for infection control management.