A Mouse Model to Assess Innate Immune Response to <em>Staphylococcus aureus</em> Infection

Abstract

Staphylococcus aureus (S. aureus) infections, including methicillin resistant stains, are an enormous burden on the healthcare system. With incidence rates of S. aureus infection climbing annually, there is a demand for additional research in its pathogenicity. Animal models of infectious disease advance our understanding of the host-pathogen response and lead to the development of effective therapeutics. Neutrophils play a primary role in the innate immune response that controls S. aureus infections by forming an abscess to wall off the infection and facilitate bacterial clearance; the number of neutrophils that infiltrate an S. aureus skin infection often correlates with disease outcome. LysM-EGFP mice, which possess the enhanced green fluorescent protein (EGFP) inserted in the Lysozyme M (LysM) promoter region (expressed primarily by neutrophils), when used in conjunction with in vivo whole animal fluorescence imaging (FLI) provide a means of quantifying neutrophil emigration noninvasively and longitudinally into wounded skin. When combined with a bioluminescent S. aureus strain and sequential in vivo whole animal bioluminescent imaging (BLI), it is possible to longitudinally monitor both the neutrophil recruitment dynamics and in vivo bacterial burden at the site of infection in anesthetized mice from onset of infection to resolution or death. Mice are more resistant to a number of virulence factors produced by S. aureus that facilitate effective colonization and infection in humans. Immunodeficient mice provide a more sensitive animal model to examine persistent S. aureus infections and the ability of therapeutics to boost innate immune responses. Herein, we characterize responses in LysM-EGFP mice that have been bred to MyD88-deficient mice (LysM-EGFP×MyD88−/− mice) along with wild-type LysM-EGFP mice to investigate S. aureus skin wound infection. Multispectral simultaneous detection enabled study of neutrophil recruitment dynamics by using in vivo FLI, bacterial burden by using in vivo BLI, and wound healing longitudinally and noninvasively over time.

Murine Models for Staphylococcal Infection

“…The purpose of this protocol is to experimentally model S. aureus subcutaneous infections. Skin and soft tissue infections (SSTIs) are the most common forms of S. aureus disease worldwide (Anderson et al, 2019;Malachowa et al, 2019). As S. aureus often breaches the epidermal layer of skin, a subcutaneous model of murine S. aureus infection allows us to consistently and safely model and study these types of infections (Brandt et al, 2018).…”

“…Currently, most animal models of Staphylococcus aureus infection aim to (1) understand the biological role of different bacterial toxins and/or virulence factors from human clinical isolates, (2) provide experimental validation for the molecular basis of pathogenesis, (3) elucidate the utility of S. aureus factors as antigens for vaccines, (4) define the molecular mechanisms whereby immunity is achieved, and (5) determine the role of antimicrobials in eliminating the infection in vivo (Abdul Hamid et al., 2020; Anderson, Reynolds, Rivara, Miller, & Simon, 2019; Guo et al., 2013; Kim, Missiakas, & Schneewind, 2014; Malachowa, Kobayashi, Lovaglio, & DeLeo, 2019). More recently, an overall increased interest in understanding the role of specific immune components (innate and adaptive arms) in the pathogenesis of the disease has emerged (Brandt, Putnam, Cassat, & Serezani, 2018; Goldmann & Medina, 2018; Krishna & Miller, 2012).…”

Staphylococcus aureus Host Tropism and Its Implications for Murine Infection Models

“…Conventional mouse models are the most frequently used systems for investigating a variety of S. aureus diseases, e.g., skin and soft tissue infections [ 77 , 78 ], bacteremia [ 79 , 80 ], sepsis [ 81 , 82 ], peritonitis [ 83 , 84 ], pneumonia [ 85 , 86 ], osteomyelitis [ 87 , 88 ], and endocarditis [ 89 , 90 ]. Although these models led to important advancements in our understanding of host–pathogen interaction, as well as to the identification of key virulence factors and potential treatment strategies for S. aureus infections, scientists have had to deal with failures of human clinical trials based on mouse models, with vaccination studies being a prime example [ 91 , 92 , 93 ].…”

Research Techniques Made Simple: Mouse Bacterial Skin Infection Models for Immunity Research

“…mouse wound infection model is performed by inoculating bacteria into full-thickness incisional cuts or excisional wounds (Dai et al, 2011). For example, incisional wounds can be inoculated with a bioluminescent S. aureus strain in lysozyme M-EGFP reporter mice to longitudinally monitor both the bacterial burden and neutrophil recruitment dynamics during the course of infection and wound healing ( Figure 2aed) (Anderson et al, 2019;Kim et al, 2008). Furthermore, histological analysis of the infected wound skin can be used to analyze neutrophil abscess area, bacterial bandwidth, and the presence of specific cells (Figure 2e) (Cho et al, 2011).…”