Oxacillin alters the toxin expression profile of community-associated methicillin-resistant Staphylococcus aureus

Area of Science:

• Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains are more virulent than healthcare-associated MRSA (HA-MRSA).
• CA-MRSA strains exhibit higher toxin expression, potentially linked to lower PBP2a and higher Agr activity.
• The type IV SCCmec element in CA-MRSA is associated with lower PBP2a expression and increased toxicity.

Purpose of the Study:

• To investigate if subinhibitory oxacillin concentrations can attenuate CA-MRSA toxicity.
• To determine the effect of oxacillin on PBP2a expression, Agr activity, and toxin secretion in CA-MRSA.

Main Methods:

• Treatment of CA-MRSA strains with subinhibitory concentrations of oxacillin.
• Measurement of PBP2a expression, Agr quorum sensing activity, and secretion of phenol-soluble modulins (PSMs), alpha-toxin, and Panton-Valentine leucocidin (PVL).
• Assessment of the net effect on cell lysis by different CA-MRSA strains under oxacillin treatment.

Main Results:

• Subinhibitory oxacillin induced PBP2a expression and repressed Agr activity, decreasing PSM secretion.
• Oxacillin increased alpha-toxin and PVL expression, consistent with other studies.
• The net effect on cell lysis was variable: reduced where PSMs and alpha-toxin were dominant, but increased where PVL was critical.

Conclusions:

• Oxacillin has a pleiotropic effect on CA-MRSA virulence factors, impacting toxin expression and secretion.
• While oxacillin can reduce toxicity by suppressing PSMs, it may enhance virulence in PVL-dependent contexts.
• The complex interplay of toxin modulation by oxacillin highlights the need for careful consideration in CA-MRSA treatment strategies.