An in vitro study on the potential of selected South African plant extracts to prevent and treat bovine mastitis

Abstract

Mastitis is a painful inflammatory condition, commonly resulting from infections caused by Staphylococcus aureus and other pathogens. In this study, antimicrobial, anti-biofilm and anti-quorum sensing activities of selected plants were investigated against Staphylococcus aureus isolates from clinical cases of bovine mastitis. Acetone and ethanol extracts of 15 plants were initially screened for their antimicrobial activities against the commercially available reference strain S. aureus ATCC 29213. Maytenus undata, Maurocenia frangula, Kalanchoe gunniae and Bryophyllum pinnatum had good activities and extracts were tested against six multi-drug resistant S. aureus strains isolated from clinical bovine mastitis cases. The four plants were further analysed for cytotoxicity and anti-quorum sensing activities. Two of the plants with good results were assessed further for anti-biofilm activity. Minimum inhibitory concentration (MIC) values of the extracts against S. aureus isolates ranged from 0.02 to 0.63 mg/mL. Kalanchoe gunniae extracts were the least cytotoxic with extremely promising selectivity index (SI) values ranging from 12 to 25. Significant inhibition of biofilm development against S. aureus mastitis isolates was observed, but extracts were not able to eradicate pre-formed biofilms. Kalanchoe gunniae extracts had the best anti-quorum sensing activity with minimum quorum sensing inhibition concentration (MQSIC) and MIC values of 0.04 mg/mL and 0.63 mg/mL respectively against Chromobacterium violaceum ATCC 12472. Therefore, K. gunniae holds potential for development of a preventative treatment against bovine mastitis.