Abstract:
Among the global health problems in the 21st century, antibiotic resistance is considered as an
exigent challenge emerged mainly due to the indiscriminate use of antibiotics during various
infectious diseases. Therefore, searching novel antimicrobial agents from various alternative
sources in the nature including ignored species such as lichens has become important. This
study investigated the in-vitro antimicrobial potential of Parmotrema tinctorum against four
medically important gram positive and negative bacterial strains. Ethanol, hexane and aqueous
extracts of the lichen were prepared according to standard protocols. Staphylococcus aureus
(ATCC 25923), Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922) and
Klebsiella pneumoniae (ATCC 700603) were used as the test organisms. Antibacterial activities were screened by agar disc diffusion assay. Minimum inhibitory concentration (MIC) was
obtained by broth micro-dilution method with cefotaxime intravenous solution as the positive
control. Only ethanol and hexane extracts were active against S. aureus. None of the extracts
were active against P. aeruginosa, E. coli and K. pneumoniae. Ethanol extract at 300 mg/ml
concentration exhibited an inhibition zone of 9.4 ± 0.1mm, while hexane extract showed 7.7
± 0.2, 7.5 ± 0.1 and 6.8 ± 0.3mm zone diameters for concentrations at 300, 30 and 3 mg/ml
respectively. The MIC values for both ethanol and hexane extracts were 2.4 mg/ml against S.
aureus. Both ethanol and hexane extracts of P. tinctorum have similar antibacterial potential
against the gram positive bacterium, S. aureus. Further studies are required to fractionate and
identify the active constituents which exhibited the antibacterial activity.
