Differences in Biofilm Formation by Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus Strains

Staphylococcus aureus (S. aureus) is a common pathogen involved in community- and hospital-acquired infections. Its biofilm formation ability predisposes it to device-related infections. Methicillin-resistant S. aureus (MRSA) strains are associated with more serious infections and higher mortality rates and are more complex in terms of antibiotic resistance. It is still controversial whether MRSA are indeed more virulent than methicillin-susceptible S. aureus (MSSA) strains. A difference in biofilm formation by both types of bacteria has been suggested, but how only the presence of the SCCmec cassette or mecA influences this phenotype remains unclear. In this review, we have searched for literature studying the difference in biofilm formation by MRSA and MSSA. We highlighted the relevance of the icaADBC operon in the PIA-dependent biofilms generated by MSSA under osmotic stress conditions, and the role of extracellular DNA and surface proteins in the PIA-independent biofilms generated by MRSA. We described the prominent role of surface proteins with the LPXTG motif and hydrolases for the release of extracellular DNA in the MRSA biofilm formation. Finally, we explained the main regulatory systems in S. aureus involved in virulence and biofilm formation, such as the SarA and Agr systems. As most of the studies were in vitro using inert surfaces, it will be necessary in the future to focus on biofilm formation on extracellular matrix components and its relevance in the pathogenesis of infection by both types of strains using in vivo animal models.