Bactericidal Activity of Carvacrol against <i>Streptococcus pyogenes</i> Involves Alteration of Membrane Fluidity and Integrity through Interaction with Membrane Phospholipids

• Main Authors: Niluni M. Wijesundara (Author), Song F. Lee (Author), Zhenyu Cheng (Author), Ross Davidson (Author), David N. Langelaan (Author), H. P. Vasantha Rupasinghe (Author)
• Format: Book
• Published: MDPI AG, 2022-09-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.
• Notes: 10.3390/pharmaceutics14101992; 1999-4923
• Keywords: carvacrol; streptococcal pharyngitis; <i>Streptococcus pyogenes</i>; mechanism of action; membrane; phospholipids; Pharmacy and materia medica; RS1-441
• Source: Pharmaceutics, Vol 14, Iss 10, p 1992 (2022)

Background: Carvacrol, a mono-terpenoid phenol found in herbs, such as oregano and thyme, has excellent antibacterial properties against <i>Streptococcus pyogenes</i>. However, its mechanism of bactericidal activity on <i>S. pyogenes</i> has not been elucidated. Objectives: This study investigated the bactericidal mechanism of carvacrol using three strains of <i>S. pyogenes</i>. Methods: Flow cytometry (FCM) experiments were conducted to determine carvacrol's membrane permeabilization and cytoplasmic membrane depolarization activities. Protoplasts of <i>S. pyogenes</i> were used to investigate carvacrol's effects on the membrane, followed by gel electrophoresis. The carvacrol-treated protoplasts were examined by transmission electron microscopy (TEM) to observe ultrastructural morphological changes. The fluidity of the cell membrane was measured by steady-state fluorescence anisotropy. Thin-layer chromatographic (TLC) profiling was conducted to study the affinity of carvacrol for membrane phospholipids. Results: Increased membrane permeability and decreased membrane potential from FCM and electron microscopy observations revealed that carvacrol killed the bacteria primarily by disrupting membrane integrity, leading to whole-cell lysis. Ultra-structural morphological changes in the membrane induced by carvacrol over a short period were confirmed using the <i>S. pyogenes</i> protoplast and membrane isolate models in vitro. In addition, changes in the other biophysical properties of the bacterial membrane, including concentration- and time-dependent increased fluidity, were observed. TLC experiments showed that carvacrol preferentially interacts with membrane phosphatidylglycerol (P.G.), phosphatidylethanolamine (P.E.), and cardiolipins (CL). Conclusions: Carvacrol exhibited rapid bactericidal action against <i>S. pyogenes</i> by disrupting the bacterial membrane and increasing permeability, possibly due to affinity with specific membrane phospholipids, such as P.E., P.G., and CL. Therefore, the bactericidal concentration of carvacrol (250 µg/mL) could be used to develop safe and efficacious natural health products for managing streptococcal pharyngitis or therapeutic applications.