Phenotypic and Molecular Detection of IMP and SPM Metallo-Beta-Lactamases in Clinical Isolates of Carbapenem Resistant Pseudomonas aeruginosa

Abstract

Objectives: Metallo-beta-lactamases play a major role in the resistance of Pseudomonas aeruginosa to carbapenems. The aim of this study was the phenotypic and molecular detection of IMP and SPM carbapenemase genes in 100 carbapenem-resistant clinical isolates of P. aeruginosa. The isolates identified using standard microbiological tests, and their antibiotic susceptibility pattern determined by disk agar diffusion (Kirby Bauer) method. Phenotypic identification of Metallo-beta-lactamase-producing strains assessed by the combined disk test (CDT). Then, PCR was used to detect the presence of IMP and SPM genes.Results: The highest and lowest levels of antibiotic resistance were observed against gentamicin (40%) and piperacillin-tazobactam (13%), respectively. Besides, 40 isolates (40%) had the Multi-drug Resistant (MDR) phenotype, while 5 (12.5%) MDR isolates were resistant to all antibiotics tested. The results of the CDT showed that among 43 carbapenem non-susceptible clinical isolates of P. aeruginosa, 33 (76.74%) isolates were Metallo-beta-lactamase-producing strains. Also, the frequency of the IMP gene was determined to be 9%, while none of these isolates carried the SPM gene. Due to the high prevalence of carbapenem-resistant and MDR P. aeruginosa in this study, routine antibiotic susceptibility testing and phenotypic identification of carbapenemase production by this bacterium are necessary for proper selection of antibiotics.