Staphylococcus aureus is a major human pathogen that causes an array of infections ranging from minor skin infections to more serious infections including osteomyelitis, endocarditis, necrotizing pneumonia and sepsis 1 . These more serious infections usually arise from an initial bloodstream infection and are frequently recalcitrant to antibiotic treatment 1 . Phagocytosis by macrophages and neutrophils is the primary mechanism by which S. aureus infection is controlled by the immune system 2 . Macrophages have been shown to be a major reservoir of S. aureus in vivo 3 but the role of macrophages in the induction of antibiotic tolerance has not been explored. Here we show that macrophages not only fail to efficiently kill phagocytosed S. aureus but also induce tolerance to multiple antibiotics. Reactive oxygen species (ROS) generated by respiratory burst attack iron-sulfur (Fe-S) cluster containing proteins, including TCA cycle enzymes, resulting in decreased respiration, lower ATP and increased antibiotic tolerance. We further show that during a murine systemic infection, respiratory burst induces antibiotic tolerance in the spleen. These Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Chronic coinfections of Staphylococcus aureus and Pseudomonas aeruginosa frequently fail to respond to antibiotic treatment, leading to significant patient morbidity and mortality. Currently, the impact of interspecies interaction on S. aureus antibiotic susceptibility remains poorly understood. In this study, we utilize a panel of P. aeruginosa burn wound and cystic fibrosis (CF) lung isolates to demonstrate that P. aeruginosa alters S. aureus susceptibility to bactericidal antibiotics in a variable, strain-dependent manner and further identify 3 independent interactions responsible for antagonizing or potentiating antibiotic activity against S. aureus. We find that P. aeruginosa LasA endopeptidase potentiates lysis of S. aureus by vancomycin, rhamnolipids facilitate proton-motive force-independent tobramycin uptake, and 2-heptyl-4-hydroxyquinoline N-oxide (HQNO) induces multidrug tolerance in S. aureus through respiratory inhibition and reduction of cellular ATP. We find that the production of each of these factors varies between clinical isolates and corresponds to the capacity of each isolate to alter S. aureus antibiotic susceptibility. Furthermore, we demonstrate that vancomycin treatment of a S. aureus mouse burn infection is potentiated by the presence of a LasA-producing P. aeruginosa population. These findings demonstrate that antibiotic susceptibility is complex and dependent not only upon the genotype of the pathogen being targeted, but also on interactions with other microorganisms in the infection environment. Consideration of these interactions will improve the treatment of polymicrobial infections.

Significance Fermentation of dietary fiber in the lower gut of humans is a critical process for the function and integrity of both the bacterial community and host cells. Here we demonstrate that two human gut commensal Bacteroides are equipped with unique enzymes that allow degradation of xylan, a common hemicellulose in human diets. Furthermore, we identify a novel carbohydrate-binding module (CBM) family that disrupts the catalytic domain of a glycoside hydrolase 10 (GH10) endoxylanase and facilitates the hydrolytic activity of the enzyme. The conservation of the unique modular architecture of the GH10 endoxylanase in the genomes of diverse Bacteroidetes suggests a critical role in fiber digestion in this phylum.