# Solithromycin mitigates Prevotella intermedia–induced methicillin-resistant Staphylococcus aureus ventilator-associated pneumonia by enhancing alveolar macrophage function

## TL;DR

Solithromycin improves survival in a mouse model of MRSA pneumonia worsened by Prevotella intermedia by boosting macrophage function.

## Contribution

Solithromycin's novel immunomodulatory role in mitigating MRSA-VAP exacerbated by P. intermedia is demonstrated.

## Key findings

- Solithromycin significantly improved survival and reduced MRSA burden in mice.
- Solithromycin enhanced macrophage recruitment and bactericidal activity against MRSA.
- RNA-seq showed upregulation of phagocytosis and bactericidal pathways with solithromycin.

## Abstract

Ventilator-associated pneumonia (VAP) is a fatal intensive care infection. VAP caused by methicillin-resistant Staphylococcus aureus (MRSA) can be exacerbated by Prevotella intermedia culture supernatant (P. int. sup.). Solithromycin (SOL), a fourth-generation macrolide, inhibits bacterial protein synthesis and modulates immunity; however, its effects on exacerbation of MRSA-VAP by P. int. sup. remain unclear. This study examined whether SOL inhibits bacterial protein synthesis by binding to the 50S ribosomal subunits in P. int. sup. and subsequently reduces the worsening of MRSA-VAP caused by P. int. sup.

BALB/cCrSlc mice received MRSA and P. int. sup. with or without sub-minimum inhibitory concentrations of SOL (P. int. sup. (SOL)) or clarithromycin (CAM; P. int. sup. (CAM)). Outcomes included survival rates, lung MRSA burden, and transcriptomics (reverse transcription polymerase chain reaction, bulk RNA sequencing [RNA-seq]). In vitro, bone marrow-derived alveolar macrophage-like cells (AMLCs) from C57BL/6J mice were infected with MRSA ± SOL; bactericidal activity and mRNA expression were measured.

P. int. sup. increased mortality, bacterial load, and neutrophilic infiltration; however, P. int. sup. (SOL) significantly improved survival rate (100%, n = 8, ****P < 0.0001), reduced MRSA burden (n = 10–11, **P < 0.01), and enhanced macrophage recruitment (n = 7–8, ****P < 0.001). P. int. sup. downregulated Ccr2 expression (n = 7–8, ***P < 0.001). RNA-seq analysis revealed P. int. sup. (SOL) upregulated macrophage phagocytosis and bactericidal pathways. SOL-pretreated AMLCs infected with MRSA exhibited reduced bacterial burden (n = 8, *P < 0.05 vs control, **P < 0.01 vs CAM-pretreated AMLCs) and upregulated Tnf-α expression (n = 7–8, *P < 0.05 vs control).

SOL protects by activating alveolar macrophages and promoting TNF-related responses, suggesting a novel immunomodulatory role for SOL in host defense against exacerbation of MRSA-VAP by P. int. sup.