Among them, 1-decanol (C10) showed highest activity against both M. smegmatis and M. tuberculosis. In addition, the current study also shows that the presence of a terminal double bond in a fatty alcohol potentiates its antimycobacterial activity. This antimycobacterial activity of the alcohols was found to be partly, if not exclusively, due to damage to the cellular envelope. The ability of 1-decanol and 9-decene-1-ol to attenuate biofilm formation by M. smegmatis was also investigated. All the alkanes, alkanols and alkene-1-ol used in this study were purchased from Sigma-Aldrich (St Louis, MO). Mycobacterium smegmatis mc2155 (ATCC 700084) and M. tuberculosis H37Rv (ATCC 25618) used in Selleckchem MAPK Inhibitor Library this study were a kind gift from Prof.
Sujoy Dasgupta, Bose Institute, Kolkata,
India, and Prof. N. K. Pal, IPGMER, Kolkata, India. Middlebrook 7H9 broth base supplemented with glycerol and bovine serum albumin was used for cultivation of M. smegmatis and Kirchner’s broth supplemented with antibiotic cocktail Polymyxin B, Amphotericin B, Carbenicillin, Trimethoprim was used for cultivation of M. tuberculosis. The medium contains phenol red as a pH indicator that turns yellow from pink upon growth of the M. tuberculosis. Preliminary assessment for antimycobacterial activity of long-chain fatty alcohols was done by agar diffusion method as described previously (Bauer et al., 1966). Briefly, paper discs of 4 mm in diameter soaked Selleckchem Proteasome inhibitor with 3 μL of each alcohol were placed on agar plates overlaid with soft agar (0.6%) that was inoculated with M. smegmatis mc2155. Plates were incubated for 48 h at 37 °C. The extent of inhibition was measured by the diameter of the zone of inhibition created around the
disc. The BDS method was performed as described previously (Charles, 1974). Briefly the compound to be tested was dissolved at a concentration of 8 mg mL−1 in 70% dimethyl sulfoxide and was further diluted twofold in each consecutive test tube in either Middlebrook 7H9 broth (Difco, Detroit, MI) for M. smegmatis mc2155 or in Kirchner’s broth for M. tuberculosis H37Rv. An aliquot (10 μL) of an BCKDHB overnight culture of either M. smegmatis mc2 155 or M. tuberculosis H37Rv (ca. 1 × 105 CFU mL−1) were added to each tube. Each culture was incubated at 37 °C for 48 h. The minimum inhibitory concentration (MIC) was defined as the lowest concentration at which there was no visible growth of the bacteria after 48 h of incubation. Mycobacterium tuberculosis growth in Kirchner’s medium is indicated by the change in colour from pink to yellow due to pH change of the medium by acid produced during growth of M. tuberculosis. The minimum concentration of agent at which no colour change of the growth medium was observed was designated as the MIC. Mycobacterium smegmatis mc2155 cells were grown to log phase and either treated with 0.8 mM of decanol for 2 h or left untreated. Cells were smeared on a glass cover slip, dried in air for 30 min and examined under AFM (Veeco, Singapore).