High level methicillin resistance correlates with reduced Staphylococcus aureus endothelial cell damage

Area of Science:

• Microbiology
• Infectious Diseases
• Bacterial Pathogenesis

Background:

• Controversy exists regarding the intrinsic virulence of methicillin-resistant Staphylococcus aureus (MRSA) versus methicillin-susceptible S. aureus (MSSA).
• Endothelial cell (EC) damage serves as a crucial surrogate marker for virulence in bloodstream infections.

Purpose of the Study:

• To investigate and compare the intrinsic virulence of MRSA and MSSA clinical isolates.
• To elucidate the relationship between methicillin resistance levels and bacterial virulence.

Main Methods:

• Assessed EC damage induced by 42 MRSA and 40 MSSA clinical isolates.
• Utilized well-characterized S. aureus laboratory strains with SCCmec mutations.
• Correlated EC damage with toxin production (α, δ, β-toxins) and oxacillin resistance levels.

Main Results:

• MRSA isolates with hospital-acquired SCCmec types I, II, or III showed significantly less EC damage than other MRSA and MSSA isolates.
• A strong inverse correlation was observed between high-level oxacillin resistance and EC damage.
• High-level oxacillin resistant strains exhibited slower growth rates.
• EC damage positively correlated with α- and δ-toxin production.

Conclusions:

• The intrinsic virulence of MRSA is comparable to or reduced compared to MSSA.
• Bacterial virulence is intrinsically linked to the level of methicillin resistance.
• Further research into MRSA pathogenesis and resistance mechanisms is warranted.