## 1 Introduction  
The ongoing healthcare problems attributed to multidrug-resistant (MDR) bacterial infections that are difficult to treat continue to plague healthcare systems globally. Methicillin-resistant _Staphylococcus aureus_ (MRSA), one bacterium causing such an infection, remains a pathogen in various regions of the world [1]. Like all MDR bacterial infections, MRSA-linked infections can be associated with extended patient hospitalization, high morbidity, and mortality, especially in immunocompromised patients [1, 2, 3]. \(\beta\)-lactam antibiotics were the preferred drugs for the treatment of infections resulting from methicillin-resistant _S. aureus_. Vancomycin, a glycopeptide, still serves as the drug of choice in the treatment of MDR _S. aureus_ infections. However, the bacterium has developed resistance to the \(\beta\)-lactams as well as vancomycin [4, 5]. Thus, there is a decrease in the number of exogenous antibiotics for treating drug-resistant infections [3]. With a diminishing number of antimicrobials of choice, researchers have called for rationalization on the use of available antibiotics. This is intended to help reduce the rate at which MDR and pan-resistant bacterial superbugs are evolving to prevent the world from being taken back to the pre-antibiotic era [6, 7]. Other suggestions are to look into alternatives to antimicrobial treatment due to bacterial resistance to systemic monotherapy that has overtaken the rate of production of new antibiotics [8]. One such alternative is the use of a combination of antibiotics [9]. It is postulated that such combined therapeutic measures could lead to successful management of patients with extreme drug-resistant (XDR) bacterial infections [10; 11; 12]. However, the double and triple combined antibiotic therapies suggested by the researchers were all colistin-based [13]. Presently, colistin is a last-line therapeutic option in the treatment of difficult bacterial infections. Besides the toxicity of the drug, there is a growing resistance to this last-line drug, as reported globally [14; 15; 16; 17]. These reports necessitate the continued search for alternative antibiotic combinations that will exclude colistin in combined therapeutic measures [18]. There are also suggestions that such antibiotic synergistic combinations might not necessarily be the optimal options because it is thought that, as treatment progresses, there will be diminishing strength in antibiotic synergism [19]. However, as the problem of difficult-to-treat bacterial superbugs persists, the attention of researchers is currently focused on the use of herbal derivatives with antimicrobial properties, with suggestions that such plants could be synergistic enhancers [20; 21]. It is thought that such combined therapy can help with expanding the spectrum of antibiotics as well as being less toxic while preventing the emergence of resistant bacteria strains [22]. Due to the expected significant advantages associated with phytotherapy, several researchers are now looking into the effectiveness of combinations of conventional antimicrobials and plant derivatives with antimicrobial properties [22; 23; 24]. This is expected to provide less toxic antimicrobial herbal alternatives that could be used as combined therapies in the treatment of XDR bacterial infections. One such plant reported by researchers in different regions of the world due to its impressive antimicrobial properties is _Nigella sativa_ (NS), or black cumin [25; 26; 27]. In our previous study, we combined _N. sativa_ with chloroquine in the treatment of malaria induced in mice with _Plasmodium berghei_[28]. The obtained results showed significant parasite clearance over a significant period, indicating that NS potentiated the effect of chloroquine when compared with chloroquine alone. Middle Eastern and Far Eastern countries have used _Nigella sativa_ oil as a natural remedy or as a condiment/spice in food and food products from ancient times.