How pathogens interact with the host is essential in identifying its control methods. In fact, over the years of evolution, bacteria have learned how to reach the host. The bacterium L.monocytogenes is one of these agents whose pathogenesis stages are well identified [17, 18]. This bacterium enters host cells with a mechanism dependent on the interaction of adhesin and receptor with a phenomenon called the zipper mechanism [17,18,19]. In the gastrointestinal tract and on the surface of epithelial cells, this phenomenon occurs for the entry of L.monocytogenes bacteria with the interaction of internalin A and E-cadherin. Internalin A as a protein has 800 amino acids containing 15 leucine-rich regions (LRR); InlA also has an inter-repeat (IR) area demonstrated rudimentary for binding the LRR repeats domain to E-cadherin. E-cadherin negotiates the construction of adherents conjunctions in a Ca2+-dependent [17,18,19].

In this study, this interaction has been used as a target for the design of a drug that may inhibit the entry of bacteria. Figure 1 shows the interaction of internalin A with E-cadherin. Docking results showed that the affinity of this interaction was − 833 Kcal/mol, and many amino acids play a role in it. This complex was introduced to the Peptiderive server, and an inhibitory peptide derived (LGSWVIPPISCPENEKGP) from the interaction of E-cadherin with internalin A was designed. The physicochemical characteristics of the designed peptide has been shown in Table 1. Also, Fig. 2 shows the spatial structure of the studied peptide. Interestingly, the results of docking the peptide in question with internalin A showed that its connection has a greater affinity than the connection of internalin a to E-cadherin (-851 Kcal/mol). The results of this connection and the residues involved in it are shown in Fig. 2.

Detailed View of the Interactions between InlA and E-cadherin (-833 Kcal/mol). Cartoon model of the 3D format (A) and interactions of InlA with the E-cadherin (B). They were interacting residues between InlA and E-cadherin

3D structure of studied designed peptide (-851Kcal/mol) (A). Cartoon illustration of 3D format and interactions of the designed peptide with the inlA (B). They interact residues between the studied peptide and inlA (C and D)

Determining the minimum inhibitory concentration of the studied peptide revealed that the designed peptide at the highest concentration (640 µg/ml) could not prevent the observable growth of bacteria. Since the studied peptide was not developed against the vital factors for bacterial survival, the results of this part were expected, and the purpose of this part was to the possible effect of the peptide in question on bacterial survival, which could affect the results of cell culture invasion.

The results of the inhibitory effect of the studied peptide in inhibiting L.monocytogenes in cell culture (Fig. 3) showed that the concentrations of 8, 16, 32, and 64 µg/ml reduced the invasion of L.monocytogenes bacteria by 19, 35.3, 51, and 80.3%, respectively, in the Caco-2 cell line (P ≤ 0.0001). The results indicated that the effect of the studied peptide had a direct relationship with the increase in its concentration.

Effect of the designed inhibitory peptide on L.monocytogenes invasion. Intracellular L.monocytogenes decline after 1 h incubation with 8, 16,32 and 64 µg designed peptide. Untreated bacteria were used as controls. The error bars indicate the SD from three replicate samples. *P ≤ 0.05; **P ≤ 0.01 using one-way ANOVA and Tukey’s test

Although the studied peptide at the highest concentration used did not completely inhibit the invasion of bacteria into the cell, the results of this part were promising.

Inhibiting the invasion of L.monocytogenes bacteria has been one of the goals of researchers so that, Saura C. Sahu, et al. showed in 2007 a Synthetic polypeptide of 30 aa encompassing Position 16 of human and mouse E-cadherin could inhibit invasion in the human-origin Caco-2 and HepG2 cell lines. They reported that the anti-invasion effect was concentration-dependent, with 100 µg peptide ml − 1 showing a 99% inhibition of invasion, whereas 10 µg ml − 1 resulted in approximately 50% inhibition [20].

Also, in 2019, an interesting study by Moloko G. Mathipa et al. showed that a Lactobacillus casei expressing internalin A and B can prevent the invasion and damage of L.monocytogenes bacteria to the Caco 2 cell line. The recombinant L. casei expressing InlAB shows potential for use as a prophylactic intervention strategy for targeted control of L. monocytogenes during the intestinal phase of infection.

The critical point in this invasion inhibition method is that the probability of developing antimicrobial resistance by bacteria is theoretically significantly lower because bacteria have been able to access the target cells through the evolution of invasion methods over hundreds of years, and the slightest change in the structure of adhesins can disrupt bacterial pathogenesis.

In the continuation of the work, the effect of the desired peptide on the biofilm formation of the studied bacteria was investigated. This case was also investigated since internalin A is essential in forming L. monocytogenes biofilm. The results of this part revealed that the designed peptide does not have many anti-biofilm properties, and only the concentrations of 32 and 64 µg slightly reduce biofilm formation (Fig. 4).

The results of the antibiofilm effects of the designed peptide in different concentrations. Untreated bacteria were used as controls. The error bars indicate the SD from three replicate samples. *P ≤ 0.05;**P ≤ 0.01 using one-way ANOVA and Tukey’s test

In the last few decades, the subject of antimicrobial resistance has questioned the extermination of bacterial diseases [21,22,23]. Antibiotic resistance owing to mutation or the addition of resistance genes may happen nevertheless of antibiotic exposure. Nonetheless, these agents generate a theatrical boost in the emersion of resistant bacteria. This highlights the need to design novel antibacterial agencies [21, 22]. Despite many efforts to improve existing antimicrobials, only a few are effective against resistant bacteria [4]. One applicable strategy to crush this trouble is the designation of conceivable bacterial targets for inventing appropriate medicinal agencies. Protein-protein interactions (PPIs) are crucial in many biological functions and are connected with cancers and communicable illnesses [24]. Consequently, targeting PPIs can be a fortunate therapeutic procedure.

The results of this preliminary study conduct that disease can be averted by preventing the interaction of microbes with host cells, and due to the spread of antimicrobial resistance, this method can be used as an alternative or supplementary method in the future.

Synthetic polypeptides can quickly be constructed and purified in large quantities, so they may help investigate the mechanisms implicated in InlA-mediated host cell invasion.