A respiratory Streptococcus strain inhibits Acinetobacter baumannii from causing inflammatory damage through ferroptosis

Background: Microecological equilibrium is essential for human health. Previous research has demonstrated that Streptococcus strain A, the main bacterial group in the respiratory tract, can suppress harmful microbes and protect the body. In this study, Streptococcus strain D19^T was isolated from the oral and pharyngeal cavities of healthy children. Its antibacterial mechanism against Acinetobacter baumannii was examined, as well as its potential to prevent inflammatory damage to cells. We evaluated the effect of the fermentation conditions of D19^T on inhibition of Acinetobacter baumannii growth; Isolation and purification of antibacterial active components of strain D19^T and molecular mechanism of inhibition of Acinetobacter baumannii; Molecular mechanism of D19^T antibacterial protein reversing cellular inflammatory injury induced by Acinetobacter baumannii.

Results: The supernatant of fermentation broth of Streptococcus D19^T was the active component against Acinetobacter baumannii, but the bacteria had no antibacterial activity. The supernatant of D19^T fermentation broth was precipitated by (NH₄)₂SO₄ solution, and the protein was the active antibacterial component. After gel filtration chromatography and anion gel filtration chromatography, the molecular weight of antibacterial protein was 53kD. D19^T antibacterial protein can improve cell membrane permeability, limit extracellular soluble protein release, inhibit Acinetobacter baumannii biofilm formation, and prevent Acinetobacter baumannii adhesion. Acinetobacter baumannii induces inflammatory damage to respiratory cells via ferroptosis, and the D19^T antibacterial protein can counteract this damage, protecting the respiratory tract.

Conclusion: Streptococcus strain D19^T, as a potential probiotic, inhibits the growth of Acinetobacter baumannii and the inflammatory damage of respiratory cells, playing a protective role in human respiratory health.