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  • Title: Antimycobacterial activity of cyclic dipeptides isolated from Bacillus sp. N strain associated with entomopathogenic nematode.
    Author: Nishanth Kumar S, Mohandas C.
    Journal: Pharm Biol; 2014 Jan; 52(1):91-6. PubMed ID: 24047443.
    Abstract:
    CONTEXT: Tuberculosis (TB) is one of the leading causes of morbidity and mortality with a global mortality rate of two million deaths per year; one-third of the world's population is infected with Mycobacterium tuberculosis. OBJECTIVE: The aim of this study was to determine the antimycobacterial activity of six diketopiperazines (DKPs) purified from a Bacillus sp. N strain associated with entomopathogenic nematode Rhabditis (Oscheius) sp. MATERIALS AND METHODS: The minimum inhibitory concentration (MIC) and minimum bactericidal concentration of DKPs were determined using the broth dilution method on Middlebrook 7H11 against M. tuberculosis H₃₇Rv. Time-kill assay was used to determine the rate of killing of M. tuberculosis H₃₇Rv by DKPs. The cytotoxicity of the DKPs was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay against the VERO cell line. RESULTS: Out of six DKP-tested cyclo-(D-Pro-L-Leu), cyclo-(L-Pro-L-Met) and cyclo-(D-Pro-L-Phe) recorded antimycobacterial activity, the cyclo-(L-Pro-L-Met) showed the highest activity and MIC values of 4 μg/ml for M. tuberculosis H₃₇Rv. The MIC value for rifampicin was 0.06 μg/ml. Growth curve study by the MIC concentration of cyclic dipeptides recorded significant inhibition when compared with control. Time-kill curve showed maximum reduction of colony count was between 3 and 5 weeks. The DKPs are nontoxic to the VERO cell line up to 200 µg/ml. The antimycobacterial activity of cyclo-(D-Pro-L-Leu), cyclo-(L-Pro-L-Met) and cyclo-(D-Pro-L-Phe) is reported in this study for the first time. DISCUSSION AND CONCLUSION: In conclusion, the potency, low cytotoxicity and selectivity of these compounds make them valid lead compounds for treatment against TB.
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