Letharia vulpina, a vulpinic acid containing lichen, targets cell membrane and cell division processes in methicillin-resistant Staphylococcus aureus.
BACKGROUND
Antibiotic resistance in humans is a major concern. Drugs that target traditional sites and pathways are becoming obsolete; thus, compounds affecting novel targets are needed. Screening lichen metabolites for antimicrobials has yielded promising antimicrobial compounds, yet their mode of action is poorly understood. Letharia vulpina (L.) Hue (Parmeliaceae) has traditionally been used to poison predators, and treat stomach disorders; more recently L. vulpina extracts have demonstrated promising antimicrobial properties.


OBJECTIVE
This study investigates the mode of action of L. vulpina acetone extract against a methicillin-resistant Staphylococcus aureus (MRSA).


METHODS
We treated MRSA with L. vulpina extracts at 1×, 5×, and 10 × MIC values (MIC = 31.25 µg/ml) for 24 h and optical density (OD660) was measured over time to determine bacteriolytic activity; counted colony forming units (CFUs) to determine time kill dynamics; the propidium iodide (PI) assay and transmission electron microscopy were used to assess membrane-damage potential, and thin-layer chromatography was used to identify secondary compounds.


RESULTS
Bacteriolytic assays showed that L. vulpina extracts, containing only vulpinic acid, do not cause cell lysis, even at 10 × MIC values but there was 92% reduction in bacterial CFUs when treated with increased concentrations of lichen extracts over 24 h at 4 h intervals. Our data indicate that the L. vulpina extract compromises membrane integrity of the MRSA isolate and disrupts cell division processes.


CONCLUSIONS
Based on this study, detailed examination of acetone extracts of L. vulpina as well as pure extracts of vulpinic acid as potential antibacterial compounds merit further study.
a Department of Biology , Brigham Young University , Provo , UT , USA .|b M. L. Bean Life Science Museum , Brigham Young University , Provo , UT , USA , and.
Gajendra
G
Shrestha
a Department of Biology , Brigham Young University , Provo , UT , USA .
Andrew
A
Thompson
c Department of Microbiology and Molecular Biology , Brigham Young University , Provo , UT , USA.
Richard
R
Robison
a Department of Biology , Brigham Young University , Provo , UT , USA .|b M. L. Bean Life Science Museum , Brigham Young University , Provo , UT , USA , and.
Larry L
LL
St Clair
D000900:Anti-Bacterial Agents / Q000302:isolation & purification / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects* / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D005663:Furans / Q000302:isolation & purification / Q000494:pharmacology*; D006801:Humans; D008011:Lichens; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000378:metabolism; D008826:Microbial Sensitivity Tests / Q000379:methods; D000068837:Parmeliaceae; D010648:Phenylacetates / Q000302:isolation & purification / Q000494:pharmacology*; D010936:Plant Extracts / Q000302:isolation & purification / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D005663:Furans; D010648:Phenylacetates; D010936:Plant Extracts; C077134:vulpinic acid
Antibiotics; MRSA; lichens; mode of action