## 4 Discussion
### Antibacterial Activity
Knowing that the NAS and STA strains are Gram-positive organisms, this observed pattern may not be due to the cell wall infrastructure of both groups of bacteria. This variation in susceptibility patterns of _S. aureus_ and NAS isolates may likely be due to the differences in the antibacterial compounds in the different extracts or samples. It might be important to isolate and investigate these compounds and co-formulate them to produce a broad-spectrum product that can be used in the management of bovine mastitis caused by these organisms. According to Table 7, NAS strains were more susceptible to the extracts over a shorter MIC range than _S. aureus_ strains, which are susceptible over a wider MIC range. This is similar also to a previous study which reported geranium oil to have a wider MIC range (0.078-1.25%) for _S. aureus_ and a narrower MIC range (0.156-1.25%) for NAS [39]. Knowing that NAS is a group of species of _Staphylococcus_, it would be expected that their susceptibility may vary more widely than the strains of _S. aureus_ which are the same species. To observe the pattern in the opposite direction suggests that the species (or strains) of NAS used in this study have a more similar structural, biochemical, and/or physiological response to the extracts than the strains of _S. aureus_ used in the study. This may suggest the possibility of extensive genetic variations among the strains of _S. aureus_ used in this study. This calls for biomolecular investigations to understand the extent of the genetic variations among strains of the same species that are responsible for their varying susceptibility to the same extract. The average MIC of the extracts against all bacteria (Table 7; column \"STA & NAS strains\") showed that only the acetone extract of _S. lancea_ showed excellent antibacterial activity (mean MIC = 0.03 mg/mL). The acetone extracts of the other plants showed only moderate activity, while the ethanol extracts of all the plants showed moderate to poor activity. The average MIC values of all the acetone extracts of each of the plants were lower than those of their ethanol counterparts, except for _E. caffra_. The average MIC value of the ethanol extract of _E. caffra_ (mean MIC = 0.18 mg/mL) for each of the bacteria appears to be less than half of the average MIC value of its acetone extract (mean MIC = 0.45 mg/mL). This is an interesting observation since, though acetone is mostly the preferred extractant due to the observed better antibacterial activity, ethanol remains the suitable solvent due to the potential to commercialize the findings of this study. This is due to the fact that ethanol is not as flammable and less dangerous to work with in large quantities compared to acetone. Moreover, ethanol is able to effectively permeate cell membranes, which facilitates the extraction of a wide range of polar and non-polar components from inside the cell, permitting the extraction of higher levels of polar and non-polar endo-cellular components [33]. Therefore, the ethanol extract of _E. caffra_ should be further investigated. The observation of better activities with the acetone extract of the other plants is consistent with various studies, which have suggested acetone to be the preferred solvent of extraction for antimicrobial investigation of plants since acetone can extract compounds of a wider range of polarity [18,19]. Against the ATCC strain of _S. aureus_, only the acetone extracts of _S. lancea_ had good activity (MIC = 0.07 mg/mL). Both ethanol and acetone extracts of the other plants showed moderate activities, except for the ethanol extracts of _P. capensis_ (MIC = 0.94 mg/mL), _Z. mucronata_ (MIC = 0.83 mg/mL), and _T. emetica_ (MIC = 0.83 mg/mL) which showed poor activities. It generally appears that the isolates were more susceptible to the extracts than the ATCC strain, which is an interesting result, while the ATCC strain was more susceptible to gentamicin (positive control) than the isolates (Tables 5 and 6).