Antibacterial MccM as the Major Microcin in Escherichia coli Nissle 1917 against Pathogenic Enterobacteria

Probiotic Nissle 1917 (EcN) possesses excellent antibacterial effects on pathogenic enterobacteria. The microcins MccM and MccH47 produced in EcN played critical roles, but they are understudied and poorly characterized, and the individual antibacterial mechanisms are still unclear. In this study, three EcN mutants (Δ , Δ and Δ Δ ) were constructed and compared with wild-type EcN (EcN wt) to test for inhibitory effects on the growth of O157: H7, (SE), and (ST). The antibacterial effects on O157: H7 were not affected by the knockout of (MccM) and (MccH47) in EcN. However, the antibacterial effect on declined sharply in EcN mutants Δ . The overexpressed gene in EcN:: showed more efficient antibacterial activity on than that of EcN wt. Furthermore, the EcN:: strain significantly reduced the abilities of adhesion and invasion of to intestinal epithelial cells, decreasing the invasion ability of ST by 56.31% (62.57 times more than that of EcN wt) while reducing the adhesion ability of ST by 50.14% (2.41 times more than that of EcN wt). In addition, the supernatant of EcN:: culture significantly decreased the mRNA expression and secretion of IL-1β, TNF-α, and IL-6 on macrophages induced by LPS. The EcN:: strain generated twice as much orange halo as EcN wt by CAS agar diffusion assay by producing more siderophores. MccM was more closely related to the activity of EcN against and MccM-overproducing EcN inhibited growth by producing more siderophores-MccM to compete for iron, which was critical to pathogen growth. Based on the above, EcN:: can be developed as engineered probiotics to fight against pathogenic enterobacteria colonization in the gut.