Abstract Rationale Ventilator-associated pneumonia (VAP) is a common and fatal pneumonia in intensive care units. VAP caused by methicillin-resistant Staphylococcus aureus (MRSA) can be worsened 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 the worsening of MRSA-VAP by P. int. sup. remain unclear. Methods BALB/c 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 (RT-PCR, bulk RNA-seq). In vitro, bone marrow-derived alveolar macrophage-like cells (AMLCs) were infected with MRSA with or without SOL (CAM); bactericidal activity and mRNA expression were measured. Results P. int. sup. increased mortality (n = 8, P 0.0001), bacterial load (n = 10-11, P 0.05), and neutrophilic infiltration (n = 7-8, P 0.05), whereas P. int. sup. (SOL) improved survival, reduced MRSA burden, and enhanced macrophage recruitment (n = 7-8, P 0.001). P. int. sup. upregulated Ly6g and downregulated Ccr2 expression (n = 7-8, P 0.05 for each). Bulk RNA-seq analysis revealed P. int. sup. (SOL) significantly upregulated macrophage phagocytosis and bactericidal pathways. SOL-pretreated AMLCs infected with MRSA exhibited reduced bacterial burden (n = 8, P 0.05) and Tnf-α expression (n = 7-8, P 0.05). Survival differences were conducted using the log-rank test. Comparisons between two groups were performed using the Mann-Whitney U-test, while those among more than two groups were analyzed with either one-way ANOVA or the Kruskal-Wallis test. Conclusions SOL protects by activating alveolar macrophages and promoting TNF-related responses, indicating a novel immunomodulatory role for SOL in host defense against the exacerbation of MRSA-VAP caused by P. int. sup. This abstract is funded by: FUJIFILM Toyama Chemical Co., Ltd.
Fukushima et al. (Fri,) studied this question.