Sub-Inhibitory Concentrations of Oxacillin, but Not Clindamycin, Linezolid, or Tigecycline, Decrease Staphylococcal...

Area of Science:

• Microbiology
• Infectious Diseases
• Pharmacology

Background:

• Staphylococcus aureus (SA) produces virulence factors like Panton-Valentine-leucocidin (PVL), alpha-hemolysin (Hla), and phenol-soluble modulins alpha (PSMα), including delta-hemolysin (Hld).
• Sub-inhibitory concentrations (sub-MIC) of clindamycin and linezolid reduce PVL and Hla expression, but their effect on PSMα and Hld is less understood.

Purpose of the Study:

• To investigate the impact of sub-MIC antibiotics (oxacillin, clindamycin, linezolid, tigecycline) on PSMα1 and Hld expression in community-acquired methicillin-resistant SA (CA-MRSA).
• To compare the modulation of PSMα and Hld expression by antibiotics with that of PVL and Hla.

Main Methods:

• Four CA-MRSA strains (USASA300 and ST80 clone) were cultured with sub-MIC antibiotics.
• mRNA levels of psmα1, pmtB, pmtR, and RNAIII were quantified using RT-PCR.
• PSMα1 and Hld protein levels in supernatants were measured by HPLC-MS.

Main Results:

• Sub-MIC oxacillin reduced PSMα1 and Hld production, partly due to mRNA variations.
• The effects of clindamycin, linezolid, and tigecycline on toxin expression were strain- and clone-dependent.
• Antibiotic effects on mRNA levels did not consistently correlate with protein expression changes; pmtB, pmtR, and RNAIII variations were insufficient to fully explain toxin modulation.

Conclusions:

• PSMα and Hld expression are modulated by antibiotics, with oxacillin showing a potential anti-toxin effect distinct from its effect on PVL and Hla.
• Antibiotic sub-MICs can differentially regulate staphylococcal toxin production, highlighting a complex interplay between antibiotics and virulence factors.
• Further research is needed to fully elucidate the mechanisms underlying antibiotic-mediated modulation of PSMα and Hld in CA-MRSA.