Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 15 4 2023 08 27 550 556 Mohammad Dalvand Applied Microbiology Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran Seyed Ali Mirhosseini Applied Microbiology Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran Kiumarss Amini Department of Microbiology, Faculty of Basic Sciences, Saveh Branch, Islamic Azad University, Saveh, Iran Soghra Khani Department of Biochemistry, Pasteur Institute of Iran, Tehran, Iran Hamideh Mahmoodzadeh Hosseini Applied Microbiology Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran Kowsar Mansoori New Hearing Technologies Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran 2023 01 18 2023 08 06 Background and Objectives: In the present study, the anti-biofilm activity of Lactobacillus rhamnosus GG and Nisin was investigated on biofilm-forming abilities of Staphylococcus epidermidis strains and the expression of the biofilm-associated genes. Materials and Methods: In this study, the standard strain of L. rhamnosus GG (ATCC 53103) and Nisin were used to assess their anti-microbial and anti-biofilm effects on S. epidermidis (RP62A). Results: The MIC and MBC analysis showed that Nisin at 256 μg/mL and 512 μg/mL, and L. rhamnosus GG at 1×107 CFU/mL and 1×108 CFU/mL have anti-microbial activity compared to the negative control respectively. L. rhamnosus GG bacteria and Nisin inhibited the biofilm formation of S. epidermidis based on optical density of at 570 nm (P <0.001). The relative mRNA expression of aap, icaA, and icaD genes was significantly reduced compared to the negative control after treating S. epidermidis with sub-MIC of Nisin (0.44, 0.25 and 0.6 fold, respectively) (P>0.05). In addition, the relative expression of aap and icaA genes, but not icaD (P>0.05), was significantly lower than the negative control (0.62 and 0.7 fold, respectively) (P>0.05), after exposure to the sub MIC of L. rhamnosus GG. Conclusion: Nisin and L. rhamnosus GG exhibit potent activity against biofilm-forming abilities of S. epidermidis and these agents could be utilized as an anti-biofilm agents against S. epidermidis infections. https://ijm.tums.ac.ir/index.php/ijm/article/view/4089 https://ijm.tums.ac.ir/index.php/ijm/article/download/4089/1599