Disruption of Functional Membrane Microdomains Enhances Methicillin-Resistant Staphylococcus aureus Pathogenesis via Hyperexpression of Hemolysins

(1) Background: methicillin‑resistant Staphylococcus aureus (MRSA) is a zoonotic pathogen, and its hemolysins serve as key virulence factors. Functional membrane microdomains (FMMs) are protein-enriching platforms and regulate diverse physiological functions by recruiting and assembling various proteins. However, whether and how FMMs regulate the hemolytic ability of MRSA remains unclear. This study aimed to investigate FMM-mediated regulation of MRSA hemolysins and the underlying mechanisms. (2) Methods: Homologous recombination was employed to generate FMM-disrupted (N315ΔfloA) and complemented (N315ΔfloA::floA) strains from the MRSA N315 wild-type strain (N315 WT). The three strains were compared with respect to hemolytic activity, transcript levels of key virulence and regulatory genes, and in vivo virulence. (3) Results: Disruption of FMMs significantly enhanced hemolytic activity compared with N315 WT and complemented strains. Meanwhile, FMM disruption repressed the two-component system genes (vraS and vraR), while activating the agr operon (agrB, agrD, agrC and agrA) and its effector molecule RNAIII, leading to upregulation of hemolysin genes (hla, hlb, hld). In vivo, N315ΔfloA infection markedly increased mortality in G. mellonella larvae and BALB/c mice, with significantly elevated pro-inflammatory factors (TNF-α, IL-6, and IL-1β) in mouse plasma. All these phenotypes were effectively reversed in N315ΔfloA::floA. (4) Conclusions: Disruption of FMMs potentiates both hemolytic activity and overall virulence in MRSA, with the potential underlying mechanism involving the VraS/R-Agr regulatory axis that drives transcriptional upregulation of hemolysin-encoding genes.