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Background:One of the most common nasocomial bacteria is methicillin resistant Staphylococcus aureus (MRSA). Today, herbal extracts like Zataria multiflora from the Lamiaceae family are increasingly used. Objectives: In this study, the antibacterial effect of Z. multiflora on 75 strains of was evaluated. Materials and Methods:The strains of Staphylococcus aureus were examined for isolation of strains. 75 out of 232 strains were diagnosed as by oxacillin 6µg /mL screening method. The extracts of Z. multiflora were prepared from dried leaves using a maceration method. The antibacterial activity of the extract with initial concentration of 200 µg /mL was determined by the micro broth dilution method. Results:The obtained results showed that the minimum inhibitory concentration (MIC) varied from 2 to 16µg /mL for strains. It inhibited the growth of S. epidermidis, S. saprophyticus and methicillin sensitive S. aureus (MSSA) by about 8-16 µg/mL. The minimum bactericidal concentration (MBC) of the extract that could destroy 62.2% strains and the other examined bacteria was 512 µg /mL or more. Conclusions: In conclusion, it seems that Z. multiflora extracts could inhibit the growth of all of the mentioned bacteria. We noticed that the bactericidal effect of Z. multiflora extracts was less than its bacteriostatic effects.

Pseudomonas aeruginosa is a non-fermenter Gramnegative rod-shaped bacterium. This bacterium is the most critical human opportunistic pathogen among the causative agents of nosocomial infections, and cause infections in urinary and respiratory tracts, soft tissues, bones, and joints [1]. Treatment of P. aeruginosa infections by conventional antibiotics is often challenging due to the development of antibiotic resistance. The bacterium is naturally resistant to narrow-spectrum penicillins, first and second-generation cephalosporins, sulfonamides, and trimethoprim. Resistance against antibiotics is mediated through different mechanisms including impermeability to antibiotics, the efflux pump system, or the production of metallo-betalactamases (MBLs) [2]. Presence of the transcriptional regulator brlR (biofilm resistance locus regulator) is one of the contributing factors to drug resistance in P. aeruginosa isolates [3]. Another mechanism that affects the tolerance of P. aeruginosa against antimicrobial agents is a multidrug efflux pump encoded by mexAB-oprM. The cytoplasmic proteins like MexA and MexB and outer membrane proteins like OprM are categorized as non-ATPase efflux pumps. MexA is a lipoprotein and a member of the membrane fusion proteins (MFP). The family MexB pumps the antibiotics out of the cell by proton motive force manner. These genes encoding these proteins are involved in the efflux of the drugs across the cytoplasmic membrane and out of the cell [4]. An extracellular matrix consisting of polysaccharides, proteins, nucleic acids, and lipids constitute the biofilm of Pseudomonads bacteria. The biofilm function is the attachment to the surface and other cells and protection of the cells from antimicrobials and the host immune system [5, 6]. Attachment of bacteria to the damaged tissues or medical devices like catheter may lead to biofilm formation, which is commonly resistant to antibiotics. In biofilms, the mechanisms of drug resistance depend on multicellular interactions. These communities are the primary cause of many persistent bacterial infections. Within biofilms, bacteria are protected from destructive effects of chemicals and become less sensitive to antibiotics than the similar planktonic forms [7, 5, 8]. Introduction: Multidrug-resistant (MDR) Pseudomonas aeruginosa isolates are among the common cause of Nosocomial infections. In P. aeruginosa infections, several genes, mexA, and mexB are involved in resistance to antibiotics and pslA, pelA and brlR contribute to biofilm formation. This study aims to investigate the prevalence of these genes in P. aeruginosa isolates and to determine their relationship with biofilm formation, antibiotic resistant, pigment production, and source of infection. Methods: We collected 63 specimens out of 90 samples from patients hospitalized in a hospital affiliated to Shiraz University of Medical Sciences. The specimens belonged to 42 men and 21 women and included urine, sputum, wound, skin, blood, body fluid, and central venous blood (CVB). The samples were cu...