However, the importance of the physiologic state of Lr (planktonic vs. biofilm) on AHR activation remains unknown.<h4>Methods</h4>In vitro experiments using intestinal epithelial cells (IEC) and in vivo experiments in premature rodents were carried out to assess the impact of planktonic- vs. biofilm-state Lr on AHR ligand production, AHR activation, and protection against NEC.<h4>Results</h4>Biofilm-state Lr was found to have increased persistence in the intestine of premature rodent pups compared to planktonic-state Lr. Here, AHR is linked to necrotizing enterocolitis.