Potential of selected South African plants in the management of bovine mastitis caused by multi-drug resistant strains of Streptococcus uberis

Streptococcus uberis is a significant pathogen causing bovine mastitis. Strains of S. uberis have shown biofilm-forming ability and alarming levels of antibiotic resistance leading to treatment failures. This study aimed to investigate the antibacterial and anti-biofilm activities of selected South African plants against isolated strains of multidrug resistant (MDR) strains of S. uberis. Plant selection was based on reported minimum inhibitory concentration (MIC) of less than 0.1 mg/mL against Staphylococcal bacteria of mastitis origin. The MIC values of acetone and ethanol extracts of four plants (Searsia lancea, Indigofera frutescens, Erythrina caffra and Antidesma venosum) were determined against seven clinical S. uberis isolates and S. uberis ATCC 700407 using a serial microdilution assay. Anti-biofilm activity and cytotoxicity in bovine dermis (BD) and Vero cells were determined using standard methods. MIC values ranged between 0.01 and 2.50 mg/mL, with the lowest MIC obtained with the acetone extract of S. lancea (0.01 – 0.09 mg/mL). Interestingly, the MDR isolates were more susceptible to the extracts than the ATCC strain. The ethanol extract of S. lancea had the highest mean selectivity index value of 25.70. The extracts were generally less toxic to BD cells than Vero cells. All the organisms demonstrated biofilm-forming ability. The acetone extract of S. lancea completely inhibited biofilm formation and disrupted preformed biofilm of S. uberis at three sub-MIC concentrations. These findings demonstrate the potential of these plants as effective ethno- therapeutic options in bovine mastitis. They are recommended for further investigation towards developing novel alternative formulations for mastitis management.

 

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Publication History

Article published online:
16 November 2023