Natural nasal microbes offer broad-spectrum antiviral protection

Respiratory viral diseases pose severe threats to animal health and global food security, especially in intensive pig farming systems. Viruses such as porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), pseudorabies virus (PRV), and porcine epidemic diarrhea virus (PEDV) cause major outbreaks, leading to high mortality in piglets, reproductive failure in sows, and enormous economic losses worldwide. Current vaccines provide only partial protection due to frequent viral mutations, limited coverage, and short-lived immunity, underscoring the urgent need for new, broad-spectrum antiviral strategies.

Now, a research team at Nanjing Agricultural University has identified a wild-type strain of Bacillus subtilis (NS12) isolated from the nasal mucosa of outdoor pigs, which demonstrates remarkable ability to colonize mucosal surfaces and directly block viral infections.

A natural probiotic shield in the nasal mucosa

Epidemiological surveillance revealed that pigs with outdoor access carried significantly fewer respiratory viruses, a phenomenon strongly correlated with the enrichment of Bacillus subtilis in the nasal cavity. By isolating and characterizing strain NS12, the team discovered that it can persist in the nasal mucosa for up to two weeks and secrete potent antiviral metabolites capable of neutralizing a broad panel of enveloped viruses.

In controlled experiments, NS12 effectively protected piglets against PRRSV and PEDV infections, reducing viral loads, alleviating tissue damage, and improving survival rates. In a mouse model, NS12 treatment provided strong protection against PRV challenge, further confirming its cross-species antiviral efficacy.

Dual antiviral metabolites: surfactin derivatives and piceatannol

The study highlights two key antiviral compounds secreted by NS12:
Novel surfactin derivatives (C16/C17) - safer and less cytotoxic than standard surfactin, these cyclic lipopeptides disrupt viral envelope phospholipid dynamics, preventing membrane fusion with host cells.

Piceatannol - a hydroxylated stilbene phenolic compound that binds viral envelope lipids, increases saturation, and reduces membrane fluidity, thereby blocking viral entry without damaging viral structure.

Together, these metabolites form a "molecular firewall" on the nasal mucosal surface, providing a direct and broad-spectrum barrier against respiratory viruses.

Toward sustainable antiviral strategies

This work demonstrates that a naturally occurring nasal probiotic can directly inhibit viral invasion through metabolite-mediated mechanisms. Unlike vaccines that target specific viral antigens, NS12 works at the level of the viral envelope, which is derived from host cells, making resistance through viral mutation far less likely."

Professor Qian Yang, corresponding author of the study

The researchers propose that Bacillus subtilis NS12 could be developed into intranasal probiotic sprays, functional feed additives, or even next-generation veterinary antivirals. Since its mechanism targets the viral envelope, the strategy also has potential applications against human respiratory viruses, such as influenza and coronaviruses.