In the present study, bactericidal potential of some lichen secondary compounds has been presented. Three lichen species namely Cladonia ochrochlora, Parmotrema nilgherrensis and Parmotrema sancti-angelii were successively fractionated in various organic solvents nhexane, ethyl acetate, acetone and methanol. The ethyl acetate fraction (10 μg/ml) of these lichen species showed promised bactericidal activity and the order of the activity of lichen species were found as P. nilgherrensis > P. sanctiangelii > C. ochrochlora. Seven lichen secondary compounds alectoronic acid, atranorin, $-collatolic acid, fumarprotocetraric acid, hypoprotocetraric acid, lecanoric acid and protocetraric acid isolated from ethyl acetate fraction of above lichen species demonstrated moderate to strong bactericidal activity with low MIC value; alectoronic acid showed MIC 21.9 μg to 162.1 μg/ml, atranorin (5 μg - 70.7 μg/ml), $-collatolic acid (8.6 μg - 245 μg/ml), fumarprotocetraric acid (24 μg - 227.3 μg/ml), hypoprotocetraric acid (12.2 μg - 278.5 μg/ml), lecanoric acid (24.6 μg - 591.7 μg/ml), protocetraric acid (18.7 μg - 740.7 μg/ml). These secondary compounds were found most effective to kill microorganisms within a period of 0 hrs to 6 hrs incubation as evident from the kinetic time kill assay study. As far as the stability of the lichen compounds for the observed activity, it was found that these compounds were stable at 4oC without loosing their bactericidal potential.
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