The pathogenic bacterium Staphylococcus aureus is the most common pathogen isolated in skin-and-soft-tissue infections (SSTIs) in the United States. Most S. aureus SSTIs are caused by the epidemic clone USA300 in the USA. These infections can be serious; in 2019, SSTIs with S. aureus were associated with an all-cause, age-standardized mortality rate of 0.5 globally. Clinical presentations of S. aureus SSTIs vary from superficial infections with local symptoms to monomicrobial necrotizing fasciitis, which can cause systemic manifestations and may lead to serious complications or death. In order to cause skin infections, S. aureus employs a host of virulence factors including cytolytic proteins, superantigenic factors, cell wall-anchored proteins, and molecules used for immune evasion. The immune response to S. aureus SSTIs involves initial responders such as keratinocytes and neutrophils, which are supported by dendritic cells and T-lymphocytes later during infection. Treatment for S. aureus SSTIs is usually oral therapy, with parenteral therapy reserved for severe presentations; it ranges from cephalosporins and penicillin agents such as oxacillin, which is generally used for methicillin-sensitive S. aureus (MSSA), to vancomycin for methicillin-resistant S. aureus (MRSA). Treatment challenges include adverse effects, risk for Clostridioides difficile infection, and potential for antibiotic resistance.

Bacterial virulence genes are often regulated at the transcriptional level by multiple factors that respond to different environmental signals. Some factors act directly on virulence genes; others control pathogenesis by adjusting the expression of downstream regulators or the accumulation of signals that affect regulator activity. While regulation has been studied extensively during in vitro growth, relatively little is known about how gene expression is adjusted during infection. Such information is important when a particular gene product is a candidate for therapeutic intervention. Transcriptional approaches like quantitative, real-time RT-PCR and RNA-Seq are powerful ways to examine gene expression on a global level, but suffer from many technical challenges including low abundance of bacterial RNA compared to host RNA, and sample degradation by RNases. Evaluating regulation using fluorescent reporters is relatively easy, and can be multiplexed with fluorescent proteins with unique spectral properties. The method allows for single-cell, spatiotemporal analysis of gene expression in tissues that exhibit complex three-dimensional architecture and physiochemical gradients that affect bacterial regulatory networks. Such information is lost when data are averaged over the bulk population. Herein, we describe a method for quantifying gene expression in bacterial pathogens in situ. The method is based on simple tissue processing and direct observation of fluorescence from reporter proteins. We demonstrate the utility of this system by examining the expression of Staphylococcus aureus thermonuclease (nuc), whose gene product is required for immune evasion and full virulence ex vivo and in vivo. We show that nuc-gfp is strongly expressed in renal abscesses, and reveal heterogeneous gene expression due in part to apparent spatial regulation of nuc promoter activity in abscesses fully engaged with the immune response. The method can be applied to any bacterium with a manipulatable genetic system and any infection model, providing valuable information for preclinical studies and drug development.

Background Global collaboration has the potential to induce a shift in research focus away from the priorities of those in low-and low-middle-income countries (LICs and LMICs). This study quantified international collaboration among surgery publications by Fellows of the West African College of Surgeons (WACS) and investigated if collaboration with upper-middle-income and high-income countries (UMICs and HICs) decreases the homophily of research focus. Methods Publications by WACS surgery Fellows from 1960 to 2019 were characterized as local WACS publications, collaborative publications without UMIC/HIC participation, or collaborative publications with UMIC/HIC participation. Research topics were determined for each publication, and topic percentages were compared between collaboration groups. Results We analyzed 5065 publications. Most (3690 publications, 73%) were local WACS publications, while 742 (15%) were collaborative publications with UMIC/HIC participation and 633 (12%) were collaborative publications without UMIC/HIC participation. UMIC/HIC collaborations contributed to 49% of the increase (378 out of 766 publications) from 2000 to 2019. Topic homophily was significantly lower between local WACS publications and collaborations with UMIC/HIC participation (differed in nine research topics) than it was between local WACS publications and collaborations without UMIC/HIC participation (differed in two research topics). Conclusions Publications without international collaboration comprise most WACS research, but the rate of UMIC/ HIC collaborations is rapidly increasing. We found that UMIC/HIC collaborations decreased the homophily of topic focus in WACS publications, indicating that global collaborations need to have greater emphasis on the priorities of those in LICs and LMICs.

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