Mode of Action and Synergy of Ceftazidime and Baicalein against Streptococcus pyogenes

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.Keywords: Streptococcus pyogenes, Cytoplasmic membrane permeability, Baicalein, Ceftazidime, Synergistic activity, Fourier Transform-infrared microspectroscopy, Transmission electron microscop

Boesenbergia rotunda (L.) Mansf. extract potentiate the antibacterial activity of some β-lactams against β-lactam-resistant Staphylococci.

OBJECTIVE: The purpose of this study was to investigate the effect of Boesenbergia rotunda (L.) Mansf. Extract (BRE) and peptidoglycan inhibitor antibiotics, either used alone or in combination against β-lactam resistant Staphylococci. METHODS: Antibacterial and synergistic activities of BRE alone and in combination with ampicillin (AMP), cloxacillin (CLX), cefazolin (CFZ) or vancomycin (VAN) were evaluated against two β-lactam-resistant Staphylococcus aureus (BRSA) and one β-lactam-resistant Staphylococcus epidermidis (BRSE). The activities were confirmed by killing curve assays. The preliminary antimicrobial action was elucidated by transmission electron microscopy (TEM) and cytoplasmic membrane (CM) permeability. RESULTS: All tested Staphylococci were inhibited by BRE at a MIC of 16μg/mL. Two BRSA strains showed high resistance to CLX, AMP, and CFZ, while BRSE was resistant to CLX and AMP. All tested isolates remained susceptible to VAN. The chequerboard assay demonstrated the fractional inhibitory concentration index (FICI) at 0.502 of the BRE and CLX combination against the BRSA strains. Killing curve determinations confirmed the antibacterial and synergistic activities. The TEM study revealed collapse of the CM in BRE-treated cells and damage of both CM and peptidoglycan in BRE plus CLX-treated cells. The CM permeability assay showed that either BRE or nisin alone, and BRE plus CLX significantly induced leakage of OD260-absorbing materials. CONCLUSIONS: The BRE potentiated β-lactams, particularly CLX against β-lactam-resistant Staphylococci by damaging the CM and peptidoglycan layer, leading to leakage of intracellular materials. The combination of BRE and β-lactams provides a potential way forward in developing a novel antistaphylococcal agent