Doctoral Dissertation Research

SEM of Staphylococcus aureus (MDR isolate) ©2005 Cassandra Quave

DOCTORAL DISSERTATION ABSTRACT

An Ethnopharmacological Approach to Multidrug-Resistant Staphylococcus aureus:
Evaluation of Italian Plants used in the Traditional Healing of Skin Disease

One-third of botanical remedies from southern Italy are used to treat skin and soft tissue infections (SSTIs). Methicillin-resistant Staphylococcus aureus (MRSA), a common cause of SSTIs, is responsible for increased morbidity and mortality from infections. Therapeutic options are limited by antibiotic resistance. Many plants possess potent antimicrobial compounds that provide effective remedies for these disorders. Validation of traditional medical practices is important for the people who rely on medicinal plants. Moreover, identification of novel antibiotics and anti-pathogenic agents for MRSA is important to healthcare on a global scale.

I took an ethnopharmacological approach to understand how Italian medicinal plants used for the treatment of SSTIs affect MRSA growth and virulence. My hypothesis was that plants used in folk remedies for SSTI would exhibit lower mammalian cytotoxicity and greater inhibition of bacterial growth, biofilm formation and toxin production in MRSA than plants used for remedies unrelated to the skin or for plants with no ethnomedical application. The field portion of my research was conducted in the Vulture-Alto Bradano area of southern Italy. I collected 104 plant species and created 168 crude extracts. In the lab, I screened samples for activity against MRSA in a battery of bioassays. Growth inhibition was analyzed using broth micro-titer assays for determination of the minimum inhibitory concentration. Interference with quorum-sensing (QS) processes, which mediate pathogenicity, was quantified through RP-HPLC of d-toxin production. Interference with biofilm formation and adherence was assessed using staining methods. The mammalian cytotoxicity of natural products was analyzed using MTT cell proliferation assay techniques.

Although bacteriostatic activity was limited, extracts from six plants used in Italian folk medicine (Arundo donax, Ballota nigra, Juglans regia, Leopoldia comosa, Marrubium vulgare, and Rubus ulmifolius) significantly inhibited biofilm formation and adherence. Moreover, plants used to treat SSTI demonstrated significantly greater anti-biofilm activity when compared to plants with no ethnomedical application. QSI activity was evident in 90% of the extracts tested and extracts from four plants (Ballota nigra, Castanea sativa, Rosmarinus officinalis, and Sambucus ebulus) exhibited a significant dose-dependent response. Some of the plant remedies for SSTI identified in this study can be validated due to anti-MRSA activity.

View a PDF of the final dissertation

Antibiotic Resistant Staphylococcus aureus

In 2003, I wrote a review paper on multidrug-resistant Staphylococcus aureus as it relates to ethnopharmacology. Click here to view a PDF of the document The Drug Resistance Paragon.

ABSTRACT
The need for structurally novel antimicrobial compounds has arisen with the alarming fast evolution of multi-drug resistant pathogens over the past twenty years. In this review, I will focus on Staphylococcus aureus, the most common nosocomial pathogen today, and frequent carrier of resistant genes for the pencillin antibiotics, tetracyclines, methicillin and now, vancomycin. Much work on the synthetic development of compounds similar to these has failed as pathogenic strains have quickly acquired resistance. Natural products, however, hold a reservoir of many structurally unique compounds and the potential for their medicinal activity has not yet been fully explored. The interdisciplinary ethnopharmacological approach to drug discovery through understanding the relationship between natural products and bacterial resistance in S. aureus will be discussed.

Keywords: antibiotic resistance, ethnobotany, ethnopharmacology, multi-drug resistance, natural products, Staphylococcus aureus