Introduction: Pseudomonas aeruginosa is a major cause of nosocomial infections. Different mechanisms of drug resistance and acquired-resistance genes from other bacteria, caused the treatment of infections of this opportunistic pathogen with serious problems. So even with the newer antibiotics, the treatment has failed. The use of medicinal plants is one way to develop antimicrobial agents. Given the widespread use of Urtica Dioica and Zataria multifloraherbs in traditional medicine and the potential effects against many infectious agents are going to eveluate the antibacterial effect of methanoland acetone extracts of Urtica Dioica and Zataria multiflora against metallo beta-lactamase producing Pseudomonas aeruginosa carring bla VIM and bla IMP genes.

Materials & methods: This study was performed from October to February year 2014 on 448 burn patients hospitalized in Shahid Motahari Hospital, Tehran. For all MBL-producing strains, antibiotic resistance by disk diffusion method were done according to CLSI guidelines.CDDT method for detection of MBL and PCR and Sequencing methods for Identification of metallo beta-lactamase gene, bla IMP and bla VIM,were used. The minimum inhibitory concentrations of antibiotics meropenem, cefepime, ceftazidime, cefotaxime, ampicillin, piperacillin/ tazobactam and ceftriaxoneand the minimum inhibitory concentration of methanol and acetone extracts of Urtica Dioica and Zataria multiflora herbs were donebased on agar dilution method.

Findings: Among 83 imipenem resistant P.aeruginosa strains, 48 (57.9%) isolates produced MBL. PCR and sequencing methods confirmed that these strains were blaIMP-1positive genes, whereas none were positive for bla (VIM) genes. Hospitalized burn patients with MBL-producing P.aeruginosainfection had 4/48 (8.3%) mortality rate. It was demonstrated that Urtica Dioica and Zataria multiflora extracts had a significant antibacterial effect on regular and IMP-producing P. aeruginosa strains.

Discussion & Conclusions: Prevalence of MBL-producing Pseudomonas aeruginosa strains among patients is high. Also due to high resistance of chemical drugs, the use of medicinal plants such as Urtica Dioica and Zataria multiflora can be a better alternative for treatment, which requires further studies. In this study the extracts of U.dioica and Z. multiflora had a high antibacterial effect against β-lactamase producing P. aeruginosa isolates.