Purpose: To investigate the antibacterial activity of baicalein used alone, or in combination with
ceftazidime, against
Streptococcus pyogenes
.
Methods: Minimum inhibitory concentration (MIC), checkerboard assay parameters, and viability curves
were determined for
S. pyogenes DMST 30653, 30654, and 30655. Cytoplasmic membrane (CM)
permeability technique, enzyme assays, transmission electron microscopy and Fourier transforminfrared
microspectroscopy were used to investigate the changes in the bacterial biomolecules.
Results: The MIC of ceftazidime and baicalein against all the
S. pyogenes strains were 0.50 and >
256.0 μg/ml, respectively. A synergistic effect against these strains was exhibited by the
ceftazidime/baicalein combination (fractional inhibitory concentration index, < 0.37). The results for the
viable counts indicate that this synergistic activity was present. Baicalein exerted inhibitory activity
against β-lactamase. Compared with the controls, combining baicalein with ceftazidime caused
peptidoglycan and morphological damage, significantly increased CM permeability and protein
concentrations, and decreased cellular fatty acid and nucleic acid concentrations.
Conclusion: Baicalein is a potential synergistic adjunct to ceftazidime for the treatment of
S. pyogenes
infections.
