Karagounis, T. K. | Search bioRxiv

bioRxiv2024

Prophage-encoded methyltransferase drives adaptation of community-acquired methicillin-resistant Staphylococcus aureus

We recently described the evolution of a community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) USA300 variant responsible for an outbreak of skin and soft tissue infections. Acquisition of a mosaic version of the {Phi}11 prophage (m{Phi}11) that increases skin abscess size was an early step in CA-MRSA adaptation that primed the successful spread of the clone. The present report shows how prophage m{Phi}11 exerts its effect on virulence for skin infection without encoding a known toxin or fitness genes. Abscess size and skin inflammation were associated with DNA methylase activity of an m{Phi}11-encoded adenine methyltransferase (designated pamA). pamA increased expression of fibronectin-binding protein A (fnbA; FnBPA), and inactivation of fnbA eliminated the effect of pamA on abscess virulence without affecting strains lacking pamA. Thus, fnbA is a pamA-specific virulence factor. Mechanistically, pamA was shown to promote biofilm formation in vivo in skin abscesses, a phenotype linked to FnBPAs role in biofilm formation. Collectively, these data reveal a novel mechanism--epigenetic regulation of staphylococcal gene expression--by which phage can regulate virulence to drive adaptive leaps by S. aureus. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=84 SRC="FIGDIR/small/589803v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@b97d6forg.highwire.dtl.DTLVardef@1da30f1org.highwire.dtl.DTLVardef@1c34311org.highwire.dtl.DTLVardef@6834df_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2023

Quorum-sensing agr system of Staphylococcus aureus primes gene expression for protection from lethal oxidative stress

The agr quorum-sensing system links Staphylococcus aureus metabolism to virulence, in part by increasing bacterial survival during exposure to lethal concentrations of H2O2, a crucial host defense against S. aureus. We now report that protection by agr surprisingly extends beyond post-exponential growth to the exit from stationary phase when the agr system is no longer turned on. Thus, agr can be considered a constitutive protective factor. Deletion of agr increased both respiration and fermentation but decreased ATP levels and growth, suggesting that {Delta}agr cells assume a hyperactive metabolic state in response to reduced metabolic efficiency. As expected from increased respiratory gene expression, reactive oxygen species (ROS) accumulated more in the agr mutant than in wild-type cells, thereby explaining elevated susceptibility of {Delta}agr strains to lethal H2O2 doses. Increased survival of wild-type agr cells during H2O2 exposure required sodA, which detoxifies superoxide. Additionally, pretreatment of S. aureus with respiration-reducing menadione protected {Delta}agr cells from killing by H2O2. Thus, genetic deletion and pharmacologic experiments indicate that agr helps control endogenous ROS, thereby providing resilience against exogenous ROS. The long-lived "memory" of agr-mediated protection, which is uncoupled from agr activation kinetics, increased hematogenous dissemination to certain tissues during sepsis in ROS-producing, wild-type mice but not ROS-deficient (Nox2-/-) mice. These results demonstrate the importance of protection that anticipates impending ROS-mediated immune attack. The ubiquity of quorum sensing suggests that it protects many bacterial species from oxidative damage.

microbiology↗