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Objective Tuberculosis is an ancient disease, in all ages, The mankind has never stopped relentless struggle against tuberculosis. Since the1940s streptomycin was used for TB treatment, followed by first-line anti-TB drugs rifampicin, isoniazid, ethambutol,only a breakthrough is in human tuberculosis control.The broad application of anti-TB drugs, as well as regular treatment must be accompanied by the generation of bacterial resistance,from the initial mono-resistanc to poly-resistance, and even multi-drug resistant and extensively drug-resistant. Dual infection of HIV and tuberculosis in recent years is rising sharply, and Faced with the HIV epidemic and the threat of drug-resistant TB, anti-TB new drugs is extremely needed. Baicalin is flavonoids of the dried root of medicinal plant Scutellaria and has a variety of efficacy, Such as antibacterial, antiviral, antioxidant, liver protection, and neuroprotective and so on. There is rare study on anti-tuberculosis role of baicalin. Based on the current drug-resistant tuberculosis situation and the side effects of anti-TB drugs, this topic draws support from vitro antibacterial test and Morphological observation for identifying antituberculosis role and mechanisms of baicalin, to explore new ideas on conbined treatment of traditional Chinese medicine and western medicine on TB, provide the basic experimental data and lay the foundation for further clinical.Methods We run baicalin Single-drug vitro antibacterial test through absolutely consistency method for obtaining MIC to assess the anti-TB effect of baicalin. FIC was calculated to evaluate the combined effect of baicalin and anti-TB drugs through baicalin with INH, RFP and EMB susceptibility testing using checker-board method.Maked baicalin which was maked with5-(6)-TAMRA SE was proceeded vitro antibacterial test to evaluate whether the inhibitory effect of baicalin changes after fluorescent labeling and prepare the fluorescent probe with pharmacological activity. LSCM scanned mycobacterium tuberculosis after maked baicalin and execute three-dimensional reconstruction to observe the site of action of marked baicalin.Results The results from108cases of baicalin single agent vitro antibacterial test showed that baicalin owns inhibitory effect against Mycobacterium tuberculosis,MIC is between0.75and12mg/ml.12mg/ml strain accounted for8.33%,6mg/ml for45.87%,3mg/ml for37.62%,1.5mg/ml for6.48%,0.75for0.93%, MIC50and MIC90are6mg/ml. Joint drug susceptibility testing results showed joint effect of baicalin with INH、RFP is mainly as synergistic or additive, however, EMB as antagonistic. Fluorescently labeled baicalin antibacterial test results showed the MIC reduced by a concentration gradient. LSCM results suggested marked baicalin entered into M.tb to react, not only adhered to surface. According CT tomography and3D reconstruction results, we consider the site of action of fluorescently labeled baicalin may be cytoplasm, and the mechanism may be associated with affecting nucleic acid metabolism, interfering with gene expression and protein synthesis.Conclusions Baicalin possesses inhibitory effect against Mycobacterium tuberculosis, MIC is between0.75and12mg/ml.12mg/ml strain accounted for8.33%,6mg/ml for45.87%,3mg/ml for37.62%,1.5mg/ml for6.48%,0.75for0.93%, MIC50and MIC90are6mg/ml.Direct inhibitory effect may be related to its olefin structure of flavone ring, the change of Glycoside may also affect its antibacterial activity, and directly or indirectly affecting the immune system may also play inhibitory effect.Joint effect of baicalin with INH and RFP is mainly as synergistic or additive, however, EMB as antagonistic, which indicate baicalin could partially reverse the resistance to INH and RFP, reduce dose and side effects and avoid or delay the emergence of clinical drug resistance. Mechanisms may involve affecting the known drug target genes, efflux pump genes. Baicalin can not reverse EMB resistance, but further increases its resistance, increases the required dose and side effects are more likely to occur. Mechanisms may involve competitive inhibition, affecting the known drug target genes, efflux pump genes or new unknown drug target genes. Fluorescently labeled baicalin antibacterial test results showed the MIC reduced by a concentration gradient, which suggest prompted anti-TB activity, there are several probability:1.Amino increases the antibacterial activity of baicalin.2. The presence of the glycoside of flavonoids is easy to weaken its activity, Amino and5-(6) TAMRA SE may weaken the stability of the glucoside keys, thereby increase the antibacterial activity of marked baicalin.3.Antibacterial activity of baicalin groups may be more than flavone ring olefin structure, perhaps baicalin carbonyl in six is associated with antibacterial activity. LSCM results suggested marked baicalin entered into M.tb to react, not only adhered to surface. According CT tomography and3D reconstruction results, we consider the site of action of fluorescently labeled baicalin may be cytoplasm, and the mechanism may be associated with affecting nucleic acid metabolism, interfering with gene expression and protein synthesis.
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