Photolysis of Staphyloxanthin in Methicillin‐Resistant Staphylococcus aureus Potentiates Killing by Reactive Oxygen Species

Abstract

Confronted with the severe situation that the pace of resistance acquisition is faster than the clinical introduction of new antibiotics, health organizations are calling for effective approaches to combat methicillin‐resistant Staphylococcus aureus (MRSA) infections. Here, an approach to treat MRSA through photolysis of staphyloxanthin, an antioxidant residing in the microdomain of S. aureus membrane, is reported. This photochemistry process is uncovered through transient absorption imaging and quantitated by absorption spectroscopy, Raman spectroscopy, and mass spectrometry. Photolysis of staphyloxanthin transiently elevates the membrane permeability and renders MRSA highly susceptible to hydrogen peroxide attack. Consequently, staphyloxanthin photolysis by low‐level 460 nm light eradicates MRSA synergistically with hydrogen peroxide and other reactive oxygen species. The effectiveness of this synergistic therapy is well validated in MRSA planktonic culture, MRSA‐infected macrophage cells, stationary‐phase MRSA, persisters, S. aureus biofilms, and two mice wound infection models. Collectively, the work demonstrates that staphyloxanthin photolysis is a new therapeutic platform to treat MRSA infections.

Photo-Disassembly of Membrane Microdomains Revives Conventional Antibiotics against MRSA

“…1B). As a result, the unsaturated tail of STX, the nine conjugated C=C double bonds, is decomposed or truncated, as confirmed by mass spectrometry (17). In contrast, when we blocked STX biosynthesis in S. aureus by knocking down CrtM, namely S. aureus ΔCrtM, its colony turns colorless and shows no detectable peaks for all three Raman bands, confirming that these Raman bands are exclusively from STX (Fig.…”

“…For example, disassembly of FMM could be further extended to revive chloramphenicol, as its resistance primarily due to the overexpression of norA-encoded multidrug-resistance efflux pumps within the microdomains (35). As STX has the antioxidant function to shield MRSA from attacks by ROS, effective STX photolysis could further render MRSA susceptible to oxidative host killing including macrophage cells and neutrophils (17). Similar to daptomycin, the modulation on cell membrane fluidity via laser treatment can facilitate non-oxidative host defense of cationic antimicrobial peptides (25).…”

“…After effective STX photolysis, its products no longer maintain the chemical structure and properties of STX. The unsaturated tail of STX is truncated as unveiled by Raman spectroscopy results; the polarity of its products becomes significantly higher than that of STX as suggested by liquid chromatography results (17). As a result, these products spontaneously tend to disperse or detach from their original membrane organization.…”

“…Considering the significance of STX virulence in a MRSA-caused disease, an optimal light source that enables efficient, fast, complete, and deep depletion of STX is of great importance. Our previous study via transient absorption microscopy suggests that STX photolysis under tightly focused laser primarily follows a second-order photolysis model due to triplet-triplet annihilation: T* + T* à R + S, where R and S represent reduced and semi-oxidized forms (17). The triplet excitons form with high yield via singlet fission when carotenoids self-assemble into multimer or aggregates on cell membrane (19).…”

Granadaene Photobleaching Reduces the Virulence and Increases Antimicrobial Susceptibility ofStreptococcus agalactiae

“…Previous experiments have demonstrated that the staphyloxanthin (STX) carotenoid pigment within methicillin-resistant S. aureus (MRSA) is capable of undergoing photolysis when exposed to 460 nm light. This results in the formation of pores within the membrane of MRSA that not only increase the susceptibility of MRSA to reactive oxygen species, but also resensitize MRSA to conventional antibiotics the bacteria was previously resistant to (25,26).…”