Salmonella Interactions with Macrophages

Project Summary Typhoidal Salmonella serovars, including Salmonella enterica serovars Typhi (STy) and Paratyphi A (SPTyA), are the culprits behind devastating human-exclusive infections known as enteric fever, causing immense global morbidity and mortality. These pathogenic microbes adeptly outmaneuver the immune system by thriving in macrophages (MΦs), a critical aspect of Salmonella’s virulence. However, our understanding of how these typhoidal Salmonella strains interact with MΦs remains limited, with most research focused on non-typhoidal S. Typhimurium (STm). This gap in knowledge spurred our investigation. To bridge this gap in knowledge, we’ve employed unbiased methodologies, including random barcode transposon-site sequencing (RB-TnSeq) library screens under infection relevant conditions, genomic comparisons across different Salmonella serovars, and transcriptional profiling of MΦs infected by STy. These approaches have allowed us to identify typhoidal-specific fitness traits and factors. Our preliminary findings suggest that essential genes governing metal homeostasis contribute to typhoidal Salmonella’s fitness in MΦs due to pseudogenization of genes functioning in similar pathways. We have designed experiments to test these hypotheses (Aim 1). Furthermore, our bioinformatics analyses have led us to a putative typhoidal-specific virulence factor, which is translocated into MΦs via a type 3 secretion system (T3SS) and is vital for intracellular replication. We will take molecular and biochemical approaches to characterize this unique virulence factor within human MΦs (Aim 2). Finally, our comparative transcriptional profiling of MΦs containing replicating vs. non-replicating STy has unveiled a distinctive phenotype for MΦs containing replicating bacteria – anti-inflammatory, M2-like MΦs marked by phosphorylated STAT3 (pSTAT3). Elevated pSTAT3 levels in STy-infected MΦs are T3SS-dependent, suggesting that STy effectors manipulate the metabolic and immune landscape of human MΦs. We are determined to uncover specific virulence factors employed by STy to shape MΦ phenotypes (Aim 3). In essence, our research delves into the intricate strategies employed by typhoidal Salmonella to manipulate the host and inform new strategies for combating this formidable pathogen effectively.