# The potential immunological mechanisms of gut microbiota dysbiosis caused by antibiotics exacerbate the lethality of influenza viruses

## TL;DR

Misuse of antibiotics during influenza infections can worsen outcomes by disrupting gut bacteria and immune responses, but combining antibiotics with antivirals can help reverse this.

## Contribution

The study reveals how antibiotic-induced gut microbiota dysbiosis worsens influenza mortality and antiviral drug efficacy through immune pathway disruption.

## Key findings

- Antibiotic pretreatment increased IAV mortality and lung injury in mice.
- Antibiotics reduced beneficial gut microbes like Lactobacillus and Bifidobacterium.
- Combining antibiotics with antivirals restored immune balance and reduced mortality.

## Abstract

Antibiotics are not recommended to treat influenza A virus (IAV). However, antibiotic misuse for IAV persists worldwide. How to scientifically use antibiotics for IAV-infected patients remains a considerable challenge.

Here, we investigated the impact of antibiotics on viral pathogenicity, pulmonary-intestinal antiviral immunity, and antiviral drug efficacy. Our findings indicated that antibiotic intervention exacerbated IAV-caused mortality and lung injury in mice, manifested as increased mortality rates, shortened survival time, aggravated pulmonary injury, and excessive inflammatory responses. Furthermore, antibiotic pretreatment significantly diminished the efficacy of antivirals. Metagenomic sequencing revealed that antibiotics reduced the diversity and abundance of beneficial gut microbiota, including Lactobacillus and Bifidobacterium, while promoting the proliferation of pathogenic bacteria such as Klebsiella pneumoniae and Escherichia coli. Mechanistically, antibiotic intervention exacerbated IAV-caused excessive inflammatory responses by the blockage of pulmonary-intestinal antiviral immune pathways, which were caused by the upregulation of PKR, RIG-I, ISG15, and TRIM25 levels while downregulating IPS-1 mRNA levels. However, it is noteworthy that the combination of antibiotics and antiviral drugs effectively offset the adverse effects of antibiotic pretreatment on influenza mortality by upregulating IPS-1 levels and partially restoring pulmonary-intestinal immune homeostasis.

Pulmonary-intestinal immune homeostasis imbalance caused by antibiotic misuse can not only markedly exacerbate the lethality of IAV, but also significantly attenuate the efficacy of antiviral drugs. A mechanistic study confirmed that gut microbes dysbiosis caused by antibiotic pretreatment exacerbates the homeostasis imbalance of host antiviral immunity by blocking the RIG/MDA5/IPS-1 antiviral signaling pathway. However, combination therapy with antibiotics and antivirals effectively reversed the fatal outcome exacerbated by antibiotic pretreatment. Collectively, our findings not only provide a scientific explanation from the perspective of antiviral immunity as to why antibiotics should not be arbitrarily used to treat viral infections but also lay the scientific foundation for the rational clinical use of antivirals and antibiotics for treating influenza.