Effects of an Herbal Formulation Ethanolic Extract on Streptococcus pyogenes: Bactericidal Activity, Biofilm Control, and Interactions with Conventional Antibiotics.

Streptococcus pyogenes is a pathogen that causes skin infections worldwide. Currently, there is growing interest in herbal formulations as potential sources of antibacterial agents. This in vitro study investigated the antibacterial and antibiofilm activities of herbal formulation ethanolic extract (HFE), alone and combined with specific antibiotics, against S. pyogenes. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of HFE were determined using the broth microdilution method. Bactericidal activity was further evaluated using time-kill assays. Bacterial cell morphology was examined using electron microscopy. The interaction between HFE and specific antibiotics was assessed using the checkerboard assay. The MIC and MBC values of HFE against S. pyogenes ATCC 19615 were 16 and 32 µg/mL, respectively, while all clinical isolates showed MIC and MBC values of 8 µg/mL. Time-kill curve analysis demonstrated HFE's bactericidal activity within 2 h and induced ultrastructural changes in S. pyogenes cells. HFE also exhibited antibiofilm activity against both biofilm formation and established biofilms. The checkerboard assay showed indifferent interactions, with a fractional inhibitory concentration (FIC) index of 0.57-3.00 for all HFE combinations against S. pyogenes. These findings suggest the potential of HFE as a natural health product for the management of S. pyogenes infections.