Precise spatial structure impacts antimicrobial susceptibility of <i>S. aureus</i> in polymicrobial wound infections.

Abstract

A hallmark of microbial ecology is that interactions between members of a community shape community function. This includes microbial communities in human infections, such as chronic wounds, where interactions can result in more severe diseases. <i>Staphylococcus aureus</i> is the most common organism isolated from human chronic wound infections and has been shown to have both cooperative and competitive interactions with <i>Pseudomonas aeruginosa</i>. Still, despite considerable study, most interactions between these microbes have been characterized using in vitro well-mixed systems, which do not recapitulate the infection environment. Here, we characterized interactions between <i>S. aureus</i> and <i>P. aeruginosa</i> in chronic murine wounds, focusing on the role that both macro- and micro-scale spatial structures play in disease. We discovered that <i>S. aureus</i> and <i>P. aeruginosa</i> coexist at high cell densities in murine wounds. High-resolution imaging revealed that these microbes establish a patchy distribution, only occupying 5 to 25% of the wound volume. Using a quantitative framework, we identified a precise spatial structure at both the macro (mm)- and micro (µm)-scales, which was largely mediated by <i>P. aeruginosa</i> production of the antimicrobial 2-heptyl-4-hydroxyquinoline N-oxide, while the antimicrobial pyocyanin had no impact. Finally, we discovered that this precise spatial structure enhances <i>S. aureus</i> tolerance to aminoglycoside antibiotics but not vancomycin. Our results provide mechanistic insights into the biogeography of <i>S. aureus</i> and <i>P. aeruginosa</i> coinfected wounds and implicate spatial structure as a key determinant of antimicrobial tolerance in wound infections.