Interactions between lipopolysaccharide and peptide bacteriocin BacSp222 influence their biological activities

This study describes the interactions between two different pro-inflammatory factors produced by bacteria, lipopolysaccharide (LPS) from Gram-negative bacteria and the peptide BacSp222 produced by a Gram-positive zoonotic strain, Staphylococcus pseudintermedius 222. We demonstrate that the mentioned molecules interact, forming a complex, and this phenomenon selectively reduces their biological activities in vitro and in vivo. Specifically, the levels of tumor necrosis factor (TNF) and nitric oxide (NO) produced by monocyte-macrophage cells were lower in samples treated with both LPS and BacSp222 compared to those treated with LPS alone. This is most likely because BacSp222 limited the ability of LPS to stimulate the TLR4 receptor. In the Galleria mellonella larvae injected simultaneously with LPS and BacSp222, the activity of hemolymph phenoloxidase, a key component of the insect immune response, was lower than that observed in larvae injected with either LPS or BacSp222 alone. Moreover, LPS inhibited the antibacterial activity of the bacteriocin, while BacSp222 limited LPS’s ability to activate a proenzyme in the Limulus amebocyte lysate test. The changes in the activities of BacSp222 and LPS were attributed to the electrostatic interactions between LPS micelles and bacteriocin molecules, resulting in a decrease in LPS aggregate size and the direct formation of a complex between them, as revealed by gel filtration and isothermal microcalorimetry.