Staphylococcus aureus manipulates osteocytes to cause persistent chronic osteomyelitis and antibiotic resistance via...

In chronic osteomyelitis, the cortical bone serves as the primary site for long-term persistence of Staphylococcus aureus (S. aureus), the present study aimed to explore the mechanisms of immune evasion and antibiotic resistance remain incompletely understood.

Clinical methicillin-resistant S. aureus (MRSA) isolates, were collected and analyzed. Panton-Valentine leukocidin (PVL) expression levels were quantified via real-time PCR. The impact of PVL on pyroptosis was evaluated by infecting osteocytes and measuring caspase-1 activation and IL-1β release. Osteoclastogenesis and pathological bone formation were examined through TRAP staining and micro-CT. To assess therapeutic potential, pyroptosis was pharmacologically induced using disodium 4,4'-dimethoxy-5,6,5',6'-dimethylene dioxybiphenyl-2,2'-disulfonate (DMB), followed by evaluation of antibiotic efficacy and bone remodeling in osteomyelitis model.

We observed in clinical cases that the survival rate of MRSA small colony variants (SCVs) in cortical bone is higher than that of non-SCV strains, with SCVs demonstrating characteristic antibiotic resistance through reduced metabolic activity. The PCR results demonstrated that compared to wild-type, MRSA SCVs exhibited significantly reduced expression levels of PVL, this low-PVL-expression phenotype markedly suppresses the activation of the pyroptosis pathway following infection. Furthermore, we discovered that during the adaptation to the intra-cortical environment, the global regulatory factor Sae and the protease aureolysin mediate the active downregulation of PVL, which resulted in targeted inhibition of osteocyte pyroptosis. The suppression of osteocyte pyroptosis simultaneously diminishes the host immune response, MRSA colonization, and antibiotics resistance. Pharmacological induction of pyroptosis via DMB significantly enhanced antibiotic efficacy, as well as alleviated pathological bone formation in chronic osteomyelitis.

MRSA modulates its own virulence factors to create a favorable space and environment for long-term survival within the cortical bone, and therapeutic strategies targeting osteocyte pyroptosis may represent a potential strategy of eradicating MRSA from cortical bone.