Antibacterial, antibiofilm, and anti-quorum sensing activities of pyocyanin against methicillin-resistant Staphylococcus aureus: in vitro and in vivo study

Background: Methicillin-resistant Staphylococcus aureus (MRSA) infections are considered a major public health problem, as the treatment options are restricted. Biofilm formation and the quorum sensing (QS) system play a pivotal role in S. aureus pathogenicity. Hence, this study was performed to explore the Antibacterial effect of pyocyanin (PCN) on MRSA as well as its effect on MRSA biofilm and QS.

Results: Data revealed that PCN exhibited strong Antibacterial activity against all test MRSA isolates (n = 30) with a MIC value equal to 8 µg/ml. About 88% of MRSA biofilms were eradicated by PCN treatment using the crystal violet assay. The disruption of MRSA biofilm was confirmed using confocal laser scanning microscopy, which showed a reduction in Bacterial viability (approximately equal to 82%) and biofilm thickness (approximately equal to 60%). Additionally, the disruption of the formation of microcolonies and the disturbance of the connection between Bacterial cells in the MRSA biofilm after PCN treatment were examined by scanning electron microscopy. The 1/2 and 1/4 MICs of PCN exerted promising anti-QS activity without affecting Bacterial viability; Agr QS-dependent virulence factors (hemolysin, protease, and motility), and the expression of agrA gene, decreased after PCN treatment. The in silico analysis confirmed the binding of PCN to the AgrA protein active site, which blocked its action. The in vivo study using the rat wound Infection model confirmed the ability of PCN to modulate the biofilm and QS of MRSA isolates.

Conclusion: The extracted PCN seems to be a good candidate for treating MRSA Infection through biofilm eradication and Agr QS inhibition.

Anti-Quorum sensing; Antibacterial; Antibiofilm; Antivirulence agent; MRSA; Pyocyanin.