Numerous studies have found that baical extract and flavonoids exert antibacterial, antiviral and antifungal actions. The antimicrobial effect of baical extract is mild and the clinical efficacy of baical in infectious diseases may be more associated with its anti-inflammatory rather than its antimicrobial activities.
Antibacterial Baical skullcap decoction was investigated for bacteriostatic and bactericidal activity against a selection of oral bacteria, including suspected periodontopathogens. At a concentration of 2%, the decoction was bacteriostatic for 8 of 11 bacteria tested, but a concentration of 3.13% or greater was required for bactericidal effect (Tsao et al 1982).
Baical aqueous-extract, but not its flavonoids, baicalin and baicalein, demonstrated antibacterial effects against the enteric pathogen Salmonella typhlmurium. The effect was compatible with commercial antibiotics including ampicillin, chloramphenicol, and streptomycin. In contrast, the growth of a non-pathogenic Escherichia coll strain was unaffected by baical (Hahm et al 2001). One study demonstrated that the addition of baical skullcap in vitro improved the responsiveness of antibiotics for the treatment of MRS A (Yang et al 2005). Antiviral Antiviral effects have been demonstrated for baical in numerous in vitro and in vivo tests. Baical extract significantly inhibit hepatitis C RNA replication in vivo (Tang et al 2003) and in vitro studies have found that:
• Intraperitoneal and intranasal administration of baical flavonoids significantly inhibits influenza virus in vivo and in vitro (Nagai et al 1989, 1992a, b, 1995a, b).
• Baical extract was bactericidal in vitro against periodontal pathogens isolated from patients with periodontal disease (Tsao et al 1982).
• Baicalein inhibits HIV-1 infection at the level of viral entry (a process known to involve interaction between HIV-1 envelope proteins and the cellular CD4 and chemokine receptors) (Li et al 2000b).
• Bacalin inhibits human T-cell leukaemia virus type I (HTLV-I) (Baylor et al 1992).
• Aqueous extract inhibits HIV type-1 protease (Lam et al 2000).
• Baicalin inhibits HIV-1 infection and replication (Li et al 1993).
• Baical flavonoids inhibit Epstein-Barr virus early antigen activation (Konoshima et al 1992).
• Wogonin suppresses hepatitis B virus surface antigen production without evidence of cytotoxicity (Huang et al 2000).
• 5,7,4'-trihydroxy-8-methoxyflavone inhibits the fusion of influenza virus with endosome/lysosome membrane (Nagai et al 1995a).
• Virus replication is suppressed, partly by inhibiting the fusion of viral envelopes with the endosome/lysosome membrane which occurs at the early stage of the virus infection cycle (Nagai et al 1995b).
• The flavones in baical have potent influenza virus siaIidase inhibitory activity and anti-influenza virus activity in vivo (Nagai et al 1992b).
• Baicalin reduces the pathogenic effects of superantigenic staphylococcal exotoxins by inhibiting the signalling pathways activated by superantigens (Krakauer et al 2001).
• Baicalin may selectively induce apoptosis of HIV-infected human T-leukaemia (CEM-HIV) cells, which have a high virus-releasing capacity, and stimulate proliferation of CEM-HIV, which have a relatively lower capacity of HIV-production (Wu et al 1995).
Antifungal Antifungal activity has been demonstrated by several studies (Blaszczyk et al 2000, Yang et al 1995). Baical extract showed clear fungistatic activities in vitro against some cutaneous and unusual pathogenic fungi, and particularly upon strains of Candida albicans, Cryptococcus neoformans and Pityrosporum ovale. The antifungal substance was isolated and found to be baicalein (Yang et al 1995). Of 56 Chinese antimicrobial plants, baical root extract had the highest activity against C. albicans (Blaszczyk et al 2000).
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