Co-culturing with Streptococcus anginosus alters Staphylococcus aureus transcriptome when exposed to tonsillar cells

Abstract

<p><i>Introduction:</i> Improved understanding of <i>Staphylococcus aureus</i> throat colonization in the presence of other co-existing microbes is important for mapping <i>S. aureus</i> adaptation to the human throat, and recurrence of infection. Here, we explore the responses triggered by the encounter between two common throat bacteria, <i>S. aureus</i> and <i>Streptococcus anginosus</i>, to identify genes in <i>S. aureus</i> that are important for colonization in the presence of human tonsillar epithelial cells and <i>S. anginosus</i>, and further compare this transcriptome with the genes expressed in <i>S. aureus</i> as only bacterium. <p><i>Methods:</i> We performed an in vitro co-culture experiment followed by RNA sequencing to identify interaction-induced transcriptional alterations and differentially expressed genes (DEGs), followed by gene enrichment analysis. <p><i>Results and discussion:</i> A total of 332 and 279 significantly differentially expressed genes with p-value < 0.05 and log2 FoldChange (log2FC) ≥ |2| were identified in <i>S. aureus</i> after 1 h and 3 h co-culturing, respectively. Alterations in expression of various <i>S. aureus</i> survival factors were observed when co-cultured with <i>S. anginosus</i> and tonsillar cells. The serine-aspartate repeat-containing protein D (sdrD) involved in adhesion, was for example highly upregulated in <i>S. aureus</i> during co-culturing with <i>S. anginosus</i> compared to <i>S. aureus</i> grown in the absence of <i>S. anginosus</i>, especially at 3 h. Several virulence genes encoding secreted proteins were also highly upregulated only when <i>S. aureus</i> was co-cultured with <i>S. anginosus</i> and tonsillar cells, and iron does not appear to be a limiting factor in this environment. These findings may be useful for the development of interventions against <i>S. aureus</i> throat colonization and could be further investigated to decipher the roles of the identified genes in the host immune response in context of a throat commensal landscape.