Reviewer response for version 2

Abstract

The emergence of multidrug resistant bacteria has driven the need for novel antibiotics. Our investigations have focussed on lichens as they naturally produce a wide range of unique and very effective defence chemicals. The aim of this study was to evaluate some of the antimicrobial properties of ten common British churchyard lichens. The lichen material was sampled from 10 species, namely Caloplaca flavescens, Diploicia canescens, Cladonia fimbriata, Psilolechia lucida, Lecanora campestris subsp. Campestris, Lecanora sulphurea, Pertusaria amara f.amara, Lepraria incana, Porpidia tuberculosa and Xanthoria calcicola. Crude acetone extracts of these lichens were tested against 6 bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonela typhimurium, Listeria monocytogenes and Lactobacillus acidophilus) and two fungi (Trichophyton interdigitale and Aspergillus flavus) by using the disc diffusion susceptibility test method. Extracts of Diploicia canescens, Psilolechia lucida, Lecanora sulphurea, Pertusaria amara and Lepraria incana showed clear inhibition of the Gram positive bacteria tested (S. aureus, L. monocytogenes, L. Plantarum). Diploicia  canescens,  Pertusaria  amara and Lepraria incana extracts also inhibited  the dermatophyte fungi tested.  Lepraria incana’s extract was the only sample tested here that showed activity against any of the Gram negative bacteria tested and that was inhibition of Pseudomnas aeruginosa. Overall, our results showed that crude extracts of Diploicia canescens and Pertusaria amara had the most potent antimicrobial activity of all the extracts tested against the organisms in these studies. This finding is in agreement with published findings elsewhere. The activity of the Porpidia tuberculosa margin material being different from that of the main colony material was an interesting and new finding