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Abstract Detail

Bryological and Lichenological Section/ABLS

Shrestha, Gajendra [1], Thompson, Andrew [2], Leavitt, Steven [3], Robison, Richard [4], St. Clair, Larry [5].

Lichen, Man’s new best friend: How simple symbionts might defeat bacterial pathogens.

The overuse and frequent misuse of antibiotic drugs have strongly selected for drug-resistant bacterial strains. Despite the continual increase in the number of drug-resistant pathogenic strains, discovery of new antimicrobial drugs is in decline. To increase the potential use-life of antimicrobials, investigations should focus on new sources of these drugs that are either opaque to pathogen resistance or express a novel mode of action. Natural products from various sources, including lichens, have yielded numerous potential antimicrobial compounds. Although there is an impressive list of reports identifying lichen-derived compounds as potentially useful antimicrobials, the mode of action of these compounds is poorly understood. In this study, we investigated the mode of action of the crude extracts of two lichen species, Letharia vulpina and Xanthoparmelia chlorochroa, against methicillin resistant Staphylococcus aureus (MRSA). Thin layer chromatography showed that L. vulpina contains vulpinic acid, whereas X. chlorochroa extracts contain usnic, salazinic, norstictic, and constictic acids. Bacteriolytic assays showed that extracts of these two lichens do not cause cell lysis, even at 10x MIC values (MIC = 31.25 µg/ml). We also found that there was a dose and time dependent reduction in the colony forming units (CFU) of bacteria with both extracts. The propidium iodide uptake assays and transmission electron micrographs (TEM) suggest that these two extracts damage MRSA cell membranes. TEM micrographs also show that the L. vulpina extract may also disrupt cell division process. Based on the results of this study we suggest that these two extracts are bacteriostatic rather than bacteriocidal, targeting cell membrane and cell division process.  

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1 - Brigham Young University, Biology, 1115 M. L. Bean Life Science Museum, Provo, UT, 84602, USA
2 - Brigham Young University, Biology, Provo, UT, 84602, USA
3 - The Field Museum, Integrative Research Center, 1400 South Lake Shore Drive, Chicago, IL, 60605, USA
4 - Brigham Young University, Microbiology and Molecular Biology, Provo, UT, 84602, USA
5 - Brigham Young University, M. L. Bean Museum, 2103C ML Bean Museum, Provo, UT, 84602, USA

Mode of action
Letharia vulpina
Xanthoparmelia chlorochroa.

Presentation Type: Oral Paper:Papers for Sections
Session: 23
Location: River Fork/Grove
Date: Tuesday, July 29th, 2014
Time: 9:00 AM
Number: 23001
Abstract ID:368
Candidate for Awards:A. J. Sharp Award

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