Screening of Antibacterial and Antifungal Activities of Six Marine Macroalgae from Coasts of Yucatán Peninsula

Agar diffusion techniques are used widely to assay plant extracts for antimicrobial activity, but there are problems associated with this technique. A micro-dilution technique was developed using 96-well microplates and tetrazolium salts to indicate bacterial growth. p-Iodonitrotetrazolium violet [0.2 mg/ml] gave better results than tetrazolium red or thiazolyl blue. The method is quick, worked well with Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, and Escherichia coli and with non-aqueous extracts from many different plants. The method gave reproducible results; required only 10-25 microliters of extract to determine minimal inhibitory concentrations, distinguished between microcidal and microstatic effects, and provided a permanent record of the results. Using S. aureus, and a Combretum molle extract, the technique was 32 times more sensitive than agar diffusion techniques and was not sensitive to culture age of the test organism up to 24 hours. The S. aureus culture could be stored up to 10 days in a cold room with little effect on the assay results. This method was useful in screening plants for antimicrobial activity and for the bioassay-guided isolation of antimicrobial compounds from plants. MIC values determined for sulfisoxazole, norfloxacin, gentamicin, and nitrofuratoin were similar to values indicated in the literature but values obtained with trimethroprim and ampicillin were higher with some bacteria.

The etiologic agents of the dermatophytoses (ringworm) are classified in three anamorphic (asexual or imperfect) genera, Epidermophyton, Microsporum, and Trichophyton. Species capable of reproducing sexually belong in the teleomorphic genus, Arthroderma, of the Ascomycota. On the basis of primary habitat association, they may be grouped as geophilic (soil associated), zoophilic, and anthropophilic. Adaptation to growth on humans by most geophilic species resulted in diminished loss of sporulation, sexuality, and other soil-associated characteristics. The dermatophytes have the ability to invade keratinized tissue (skin, hair, and nails) but are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate viable tissue of an immunocompetent host. However, invasion does elicit a host response ranging from mild to severe. Acid proteinases, elastase, keratinases, and other proteinases reportedly act as virulence factors. The development of cell-mediated immunity correlated with delayed hypersensitivity and an inflammatory response is associated with clinical cure, whereas the lack of or a defective cell-mediated immunity predisposes the host to chronic or recurrent dermatophyte infection. Chronic dermatophytosis is mostly caused by Trichophyton rubrum, and there is some evidence that mannan produced by this fungus suppresses or diminishes the inflammatory response. Since dermatophytes cause a communicable disease, modes of transmission and control are discussed as well as a survey of recent trends in therapy. Collection of specimens, culture media, and tests for identification are also presented. Genetic studies have led to an understanding of incompatibility mechanisms, pleomorphism and variation, resistance to griseofulvin, and virulence. Molecular biology has contributed to our knowledge of the taxonomy and phylogenetic relationships of dermatophytes.

Crude extracts from 21 South African medicinal plants, traditionally used for ailments of an infectious or septic nature, were screened for in vitro antibacterial activity using the agar diffusion and dilution methods. Almost all the activity exhibited was against Gram-positive bacteria, with 12 of the 21 plant species tested showing some activity against Bacillus subtilis. Only the Warburgia salutaris methanol extract inhibited the growth of Escherichia coli. None of the extracts had any activity against Klebsiella pneumoniae. The highest activity was found in the methanol extracts from Bidens pilosa, Psidium guajava, Artemisia afra and Warburgia salutaris. The majority of the antibacterial activity was present in the methanolic, rather than the aqueous extracts.