## 4 Discussion  
The MRSA isolates examined here were extremely drug-resistant and fit into the classification of XDR, as they were resistant to aminoglycos, \(\beta\)-lactams, fluoroquinolones, macrolides, and tetracycline [39; 40; 41]. However, this study has shown that _Nigella sativa_ (NS), a naturally derived herbal product, inhibits the growth of these XDR MRSA isolates, thereby confirming earlier findings. This suggests that NS derivatives could serve as possible alternatives in the management of extreme drug-resistant (XDR) MRSA isolates. The inherent antimicrobial potential of NS derivatives had been reported as equally effective as that of clinically available antibiotics [26; 32; 42]. All these reports demonstrated better inhibition of MRSA isolates by NS as compared to commonly used antibiotics, as also seen in the present study. In this investigation, the isolates responded differently to various concentrations of NS, as seen in the exhibited zones of inhibition. Additionally, although there were differences among the isolates in zones of inhibition, all NS concentrations, including the lowest concentration of 0.1 \(\mu\)g/mL, were able to hinder bacterial growth, a finding that is similar to earlier reports [32; 43]. Differences in zones of inhibition could be attributed to phenotypic differences in the MRSA strains. However, that the lowest concentration of NS exhibited growth inhibition against the isolates in this study points to its effectiveness as a potential antimicrobial. The study also shows the time-kill kinetics for the MRSA strains used in this study to be more rapid in NS and \(\beta\)-lactam combined therapies than with NS alone. This suggests the possibility of a combined additive effect or potentiation of NS to those of the antibiotics that the MRSA isolates had previously been resistant to. These findings are in agreement with earlier suggestions for the need to develop a synergistic herbal drug product that could be suitable for use in combined therapeutic measures to combat the scope of bacterial resistance [44; 45; 46]. Phytotherapy combinations with proven synergistic efficacy would not only have a multi-targeted mechanism of action but could be a main tool in delaying, alleviating, or reducing resistance to existing antimicrobials [32; 44]. Additionally, our findings show NS synergistic activity in combination with OXA, AUG, and CEF against XDR MRSA isolates, with the best effect seen in the NS-AUG combination as opposed to NS-OXA and NS-CEF, similar to an earlier report [32]. This reported that, in NS \(\beta\)-lactam synergism, there was a reversal in resistance to augmentin by MRSA, findings that are similar to those of this investigation. An earlier report on the synergistic effects of combining the by-products contained in the plant with conventional antimicrobial drugs found improved effects compared to antimicrobials alone [47]. This might explain why all NS \(\beta\)-lactam combinations were more effective than NS or the antibiotic alone. On the other hand, that the combination of 0.5 mg/mL NS and \(\beta\)-lactam showed varying results (Figure 3D-F), with complete killing seen with MRSA 1, suggests that differences in bacterial strains could be a contributory factor, as had been reported previously [25]. Figure 7: Chromatogram of \(N\). _Sativa_ oil characterized by GC-MS analysis. However, that there was better killing against the same MRSA 4 and 5 isolates (Figure 3E,F) in the 7.5 ug/mL NS and antibiotic combinations could point to a dose-dependent NS concentration, a view expressed earlier [32]. Molecular insight was gained by examining the probable mechanism of action of NS alone and with \(\beta\)-lactam antibiotic combinations using SEM and TEM techniques. A SEM micrograph analysis showed bacterial cell aggregation without the usual well-defined clustering of \(S\). _aureus_. This finding is consistent with previous studies that reported the effect of antibiotics on bacterial cells [48; 49].