Nowadays, emergence and prevalence of MRSA (Methicillin Resistant Staphylococcus aureus) strain have become a great global concern in  st century, so, it is necessary to discover new antibiotics against this pathogen. Th e aim of this study was isolation and evaluation marine bacteria from the Persian Gulf in order to fi nding antibiotic compounds against some pathogenic bacteria. For this purpose, water and sediment samples were collected from the Persian Gulf during March to October . Th e antibacterial activity of the isolated bacteria was assessed using disc diff usion method. Th e Growth Curve Interference (GCI) parameter against MRSA was determined for the high potential antibiotic producing strain. Th e most important factors aff ecting fermentation conditions in antibiotic production were also optimized. Defi nite identifi cation of intended isolate was confi rmed by S rRNA sequencing. Altogether,  bacterial colony was isolated and among them only  bacterium showed antibacterial activity. Pseudoalteromonas piscicida PG- isolated from a sediment sample was chosen as the best antibiotic producing strain. Th is strain was eff ective against all tested Gram-positive bacteria, had good anti-MRSA activity and also GCI value against MRSA was two times lower than MIC value. Among the optimized fermentation parameters, carbon and nitrogen sources play major role in effi cacy of optimized antibiotic production. Ultrastructural study on the eff ect of intended antibiotic compounds on MRSA using TEM revealed that the target site for this compound is cell wall. Considering the antibacterial eff ect of PG- strain especially against MRSA, intended antibiotic compounds can gives hope for treatment of diseases caused by multi-drug resistant bacteria.

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