Antibacterial activity

Tuberculosis is the second commonest cause of death worldwide. Thirty-two percent of the world's population is infected with Mycobacterium tuberculosis, the main cause of tuberculosis. Most forms of active tuberculosis can be treated with 6 months of medication. Unfortunately, outbreaks of multidrug resistant tuberculosis have been occurring since 1990s. Natural products form one avenue in the search for new antituberculosis agents. Recently, marine algae have become targets for screening in search of novel compounds of potential medical value. It has been reported that saringosterol had been isolated from brown algae Sargassum ringgoldianum and had antitubercular activity (Ikekawa et al., 1968). Its minimum inhibition concentration (MIC) against M. tuberculosis H37Rv was determined as 0.25 mg/ml, which is the lowest value found for plant-derived natural products, compare to the tuberculosis drug rifampicin that was determined as 0.25 mg/ml of MIC in same assay. In addition, low concentration of saringosterol showed no toxicity against in the monkey kidney epithelial (Vero) cells. Sargosterol showed half maximal inhibitory concentration (IC50) of RS mg/ml on Vero cells. The sargosterol isolated from Lessonia nigrescens are both 1:1 mixture of 24S and 24R epimers. Individual isomers were separated by normal-phase high-performance liquid chromatography (HPLC). In the antitubercular assay, the 24R isomer was found eight times more active against M. tuberculosis H37Rv with MIC of 0.125 mg/ml than that of the 24S isomer which had a MIC of 1 mg/ml. Saringosterol could be considered as an excellent lead compound due to its activity, specificity, and low toxicity (Wachter et al., 2001). Recently, 15 algae extracts were screened antibacterial activity and it was found that extracts from Isochrysis galbana inhibited multidrug resistant (MDR) M. tuberculosis. Screening on seven isolated MDR M. tuberculosis, which resisted more than three antibacterial drugs, extract from 1. galbana showed the MIC of 50 mg/ml compare to those of the tuberculosis drugs rifampicin (40 mg/ml), amikacin (700 mg/ml), streptomycin (4 mg/ml), p-amino salicylic acid (2.5 mg/ml), and isoniazid (0.2 mg/ml). Thirteen unsaturated sterols with three major sterols such as 24-oxocholesterol acetate, ergost-5-en-3 p-ol, and chol-est-5-24-1,3-(acetyloxy)-,3p-ol have been purified (Prakash et al., 2010).

This finding indicated the presences of sterols may have effect on MDR M. tuberculosis. Therefore, marine algal sterols have potential in the development of urgently needed tuberculosis drugs.

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