en aquaculture aquaculture پژوهشي Orginal research papers Lactic acid bacteria are the most common bacteria which have been introduced as probiotic. This study aimed to investigate the impacts of isolated lactic acid bacteria from the <em>Rutilus kutum</em> gut&nbsp;&nbsp; on <em>Escherichia coli</em> and <em>Pseudomonas aeruginosa</em>. Lactic acid bacteria were isolated from the intestine of 100 fish which are randomly collected from the Caspian Sea and their primary probiotic properties were evaluated based on resistance to acid, bile salts and antibiotics. The inhibitory effect of the bacteria was evaluated on <em>Escherichia coli</em> and <em>Pseudomonas aeruginosa</em>, using the agar disk diffusion method. The specific band was triggered using PCR primers for 16S rRNA gene and validated via sequencing and comparing its sequence with those of gene bank databases. In this case, <em>Lactobacillus acidophilus </em>(54.79%), <em>Lactobacillus plantarum </em>(24.65%), and <em>Lactobacillus brevis </em>(20.54%) were detected<em>. </em>The isolated bacteria were resistant to vancomycin. The most inhibitory effect belonged to <em>Lactobacillus acidophilus </em>sp. on <em>E. coli</em> and <em>P. aeruginosa</em>; with the inhibition zone of 12 and 14 mm, respectively. <em>Lactobacillus plantarum </em>had moderate inhibitory effect on <em>P. aeruginosa </em>while<em> Lactobacillus brevis</em> had neither effect on <em>E. coli</em> nor <em>P. aeruginosa</em>. Lactobacillus, Probiotic properties, Rutilus kutum, PCR 3086 3097 http://jifro.ir/browse.php?a_code=A-10-3308-1&slc_lang=en&sid=1 O. Khanmohammadi Otaghsara bio_kh@yahoo.com 100319475328460038370 100319475328460038370 No Department of Marine Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran Sh. Jamili shahlajamili45@yahoo.com 100319475328460038371 100319475328460038371 Yes Iranian Fisheries Research Institute, Agricultural Research, Education and Extension Organization, Tehran, Iran M. Alipour alipourrna@yahoo.com 100319475328460038372 100319475328460038372 No Department of Biology, Islamic Azad University (IAU) - Babol Branch, Babol, Iran. Sh. Ghobadi Shgh_science@yahoo.com 100319475328460038373 100319475328460038373 No Department of Fishery, Islamic Azad University (IAU) - Babol Branch, Babol, Iran.