Pseudomonas aeruginosa is one of the most important causes of nosocomial infection which due to extended spectrum-beta lactamases (ESBLs) and metallo-beta lactamase (MBL) producing strains is resistant to a wide range of antibiotics. The aim of this study was to detect ESBL and MBL producing P.aeruginosa isolated from patients and investigate the effects of methanol extracts of Zataria multiflora, Myrtus communis, and Peganum harmala on them. Materials and Methods: In this experimental study,

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... mples were obtained from 245 patients, referring to Shafa Hospital, Kerman, Iran. ESBLs producing strains were detected by double disk synergy test and phenotypic confirmatory test. In addition, E-test strips were used for MBL detection. P.aeruginosa MIC was determined for cefotaxime, ceftazidime, azteronam, imipenem, and meropenem. Methanol extracts of Zataria multiflora, Peganum harmala, and Myrtus communis plants were prepared by Agar perculation method. Results: Out of 245 patients referring to the burn unit, 120 P.aeruginosa isolates were detected from which 41 contained ESBL but they lacked MBL. 60% of isolates were resistant to cefotaxime, 66% to ceftazidime, 42% to azteronam, 3% to imipenem, and 5% to meropenem. Among the extracts, Zataria multiflora had the highest antibacterial effect on standard strains of P.aeruginosa in comparison with Peganum harmala and Myrtus communis. Conclusion: The prevalence of ESBL producing P.aeruginosa strains is high. In addition, noticing their high antibiotic resistance, utilization of herbs, such as Zataria multiflora may be considered an appropriate alternative for treatment; however, more investigations are needed.