Discipline: mastitis; Key words: bovine mastitis, ethnoveterinary medicine, antibacterial activity, cytotoxicity.
The continuous use of antibiotics in the treatment of mastitis has led to multidrug resistant organisms, for example methicillin-resistant Staphylococcus aureus, and vancomycin resistant S. aureus and Enterococcus. This results in the use of high doses of antibiotics in dairy cows, which may lead to increased amounts of antibiotic residues in milk which is potentially hazardous to human health. The increased antibiotic resistance of mastitis pathogens, the high expenses incurred by farmers and risks posed to human health, demonstrate a need for alternative treatments which are affordable, sustainable and more environmentally friendly. Phytotherapy using medicinal plants is one possibility in alternative treatment. Medicinal plants have been used for a variety of purposes, including food preservation, pharmaceuticals and as natural therapies for many years. They have also been used as natural antioxidants, antibacterial, cytotoxic, antiviral and fungicidal agents and nutrients. Antimicrobials obtained from plants have therapeutic potential and are effective in the treatment of infectious diseases in animals as well as humans. They may also simultaneously mitigate many of the side effects that are associated with synthetic antimicrobials, for example drowsiness and death of red blood cells.
To study the therapeutic potential further, the authors cited below selected four plant species to evaluate their antibacterial activity against a panel of microorganisms implicated in causing mastitis. These species were chosen on the basis of previously reported antibacterial activity as well as their potential use in ethnoveterinary medicine for the treatment of various diseases. The list includes Acacia nilotica (bark and leaves), Aloe arborescens (leaves) Tetradenia riparia (flowers and leaves) and Crassula multicava (whole plant).
The plant species were selected on the basis of their known antibacterial activity, use in ethnoveterinary medicine and their ready availability for in vitro testing against a panel of bacterial species implicated in causing mastitis (both ATCC strains and clinical isolates). Water and acetone extracts were prepared from the various plant parts selected. Antimicrobial activity was determined using a serial micro-dilution assay and cytotoxicity was evaluated against a mammalian kidney cell line using a tetrazolium-based colorimetric assay.
A. arborescens and C. multicava were not generally active against the tested bacteria. Acetone extracts of A. nilotica bark and T. riparia flower extracts were most active against Gram-positive bacteria. Activity against Gram negative species, notably Proteus vulgaris and Enterobacter aerogenes, was also recorded with MIC values as low as 0.0195mg/ml. The best selectivity index (SI) value of 4.22 was obtained by the T. riparia flower acetone extract against the field strain of Streptococcus uberis. Although a degree of toxicity to mammalian cells was noted in most of the extracts, SI values above 1 indicate that antibacterial activity was greater than cellular toxicity for some extracts, a preliminary indication of safety. These extracts, or purified active compounds derived from them, may prove useful in further investigations of alternative mastitis treatments.
P. Sserunkuma, L.J. McGaw, I.V. Nsahlai & J. Van Staden, 2017. Selected southern African medicinal plants with low cytotoxicity and good activity against bovine mastitis pathogens. South African Journal of Botany 111, 242–247