LAUSR

OBJECTIVES Infection with a typical community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), the USA300 clone, has become a worldwide epidemic. The formation of biofilms at the site of infection is one of the reasons for the development of intractable infectious diseases resulting from this clone. Here, we evaluated the in vitro anti-biofilm effects of anti-MRSA agents to identify the most effective agent against the USA300 clone embedded in biofilms. METHODS Vancomycin, teicoplanin, daptomycin, arbekacin, and tigecycline were used as anti-MRSA agents. The biofilm permeability of the anti-MRSA agents was assessed using a biofilm-coated Transwell. The morphological and compositional effects of anti-MRSA agents against biofilms were analyzed based on the distribution of fluorescence intensity using confocal laser microscopy. The bactericidal activities of the anti-MRSA agents against biofilm-embedded S. aureus were compared. RESULTS The permeability rates of linezolid (93.1%), daptomycin (91.3%), arbekacin (87.1%), and tigecycline (99.7%) for biofilms formed by the USA300 clone were found to be significantly higher than those of vancomycin (64.9%) and teicoplanin (62.3%) (P <  0.01). Confocal microscopic analysis showed that daptomycin greatly changed biofilm morphology (decreased thickness and increased roughness) and markedly reduced the area occupied by the biofilm. Furthermore, daptomycin effectively reduced the extracellular DNA of biofilms and showed highest bactericidal activity against biofilm-embedded USA300 clone among the anti-MRSA agents. CONCLUSION The findings from this study demonstrate that, of the tested anti-MRSA agents, daptomycin is the most effective against a biofilm-embedded USA300 clone in vitro.