Adhesion mechanism of Lactiplantibacillus plantarum 2025 and its probiotic properties against Campylobacter jejuni

Some cell surface proteins of bacteria mediate bacterial adhesion to host surfaces. This is a crucial first step in bacterial colonisation of the gastrointestinal tract and is essential for probiotic bacteria to exert their beneficial effects. Probiotics can help protect the host from pathogens by competition for available niches. Due to increasing antibiotic resistance, probiotics are considered as an alternative to antibiotics to combat pathogenic infections.

In the current study, the adhesive and probiotic characteristics of Lactiplantibacillus plantarum 2025 were investigated. Using genome analysis of L. plantarum 2025, three genes fbp, cbp and hyp were selected for study. These genes encode a fibronectin binding protein (FBP), a collagen binding protein (CBP) and a hypothetical protein (HYP) predicted to bind both fibronectin and collagen. Several additional adhesion-related genes were also found in the genome.

 The proteins FBP, CBP, and HYP were expressed in NEBExpress competent E. coli (high efficiency) cells. Both CBP and FBP were successfully purified in stable forms, while HYP was degraded during expression and was not further analysed. ELISA experiments were conducted to assess recombinant FBP and CBP binding to fibronectin and collagen I, both of which are components of the epithelial lining of the gastrointestinal tract. The results showed that FBP bound to fibronectin in a dose dependent manner, while CBP bound to collagen I in a dose dependent manner.

Bacterial binding assays demonstrated that L. plantarum 2025 binds to both fibronectin and collagen I in a dose-dependent manner. Additionally, the gastrointestinal pathogen Campylobacter jejuni strains 11168H, 81-176, and G1 also bound to fibronectin and collagen I in dose dependent manner.

Competitive binding assays were performed to determine whether L. plantarum 2025 and its adhesins in the form of recombinant proteins could compete for binding sites and prevent attachment of C. jejuni strains to fibronectin and collagen I. Both FBP and CBP reduced the binding of C. jejuni strains to fibronectin and collagen I, respectively. Similarly, in competitive binding assays, whole L. plantarum 2025 cells decreased the binding of C. jejuni strains to fibronectin by 51% to 56% and to collagen I by 48% to 51% across all strains tested.

Exclusion assays were performed to determine whether pre-attached L. plantarum 2025 to fibronectin and collagen I could prevent binding of C. jejuni strains. Pre-incubation of L. plantarum 2025 with these substrates resulted in a reduction of C. jejuni strains binding to fibronectin by 66% to 72% and to collagen I by 55% to 61%. Together, these findings demonstrate the adhesive properties of L. plantarum 2025 and suggest that FBP and CBP may mediate L. plantarum 2025 adhesion to fibronectin and collagen I. Both FBP and CBP may contribute to the ability of L. plantarum 2025 to competitively exclude C. jejuni strains. This highlights the potential of L. plantarum 2025 as a probiotic capable of interfering with pathogen colonisation of the gastrointestinal tract.