The death rate due to infectious diseases is increasing in the world, and they are still considered a great threat to humans (Liu et al., 2022). Bacterial infections have a great impact on public health, and constitute 38% of human pathogens (Lindahl and Grace, 2015). Also, fungal infectious diseases have increased in recent years (Cowen et al., 2015, Maryin and Mannino, 2003). After the golden era of antibiotics, a 40-year period of inactivity in this industry was observed, while recently, the pharmaceutical industry was more focused on chemically modifying previous antibiotics (Abdallah et al., 2023, Klug et al., 2021, Boyd et al., 2021). However, due to developing antimicrobial resistance, there are not enough antibiotics to meet the current and future needs of patients (Kzhyshkowska et al., 2022, Zetts et al., 2020). Also, increasing use of common antibiotics can cause to increased resistance rates of pathogenic microbial species, causing the serious global health problems and economic cost (Organisation, 2020). It is estimated that the antimicrobial resistance associated mortality will reach 10 million people per year by 2050 (De Kraker et al. 2016). On the other hand, high level resistance of pathogenic fungi to antifungal agents along with their toxicity to human cells have been presented as the main problems in the treatment of fungal diseases (Fisher et al., 2018). The rapid development of multiple resistance to antibiotics prompts scientists to look for new solutions and even go back to the pre-antibiotic era (Brown and Wright, 2016).

Due to their antimicrobial properties, medicinal plants were used to treat infectious diseases before the advent of antibiotics (Cowan, 1999, Emeka et al., 2012). Angiosperms are about 250 000 to 500 000 years old and many of them are used for medicinal purposes (Cowan, 1999). Ancient medicine has reached us through tablets containing the names of herbal medicines, which the oldest belong to the Sumerians (Pan et al., 2014). The people living between Tigris and Euphrates rivers used certain plants to treat their diseases, and the Chinese believed that nature has a cure for every pain (Pan et al., 2014). Iranians have also had advanced knowledge in the field of medicinal plants and their therapeutic application for a long time (Petrovska, 2012). For these reasons, the use of medicinal plants is increasing worldwide for the treatment of infectious diseases and reducing the concerns caused by antibiotic resistance (Ekor, 2014). The use of medicinal plants has taken a significant part in health care both in developing and developed countries as complementary medicines (Ekor, 2014). Many studies have been conducted to investigate the antimicrobial properties of compounds derived from medicinal plants between 2010 and 2022 in order to prevent the emergence of drug-resistant microbes (Abdallah et al., 2023).

One of these plants that has medicinal properties is the toothbrush plant with the scientific name Salvadora persica L. from the Salvaduraceae family (Noumi et al., 2010, Al-Bayati and Sulaiman, 2008). The essential oil and extract of this plant contain several compounds such as benzyl isothiocyanate, trimethylamine, fluoride, fluorine, eugenol, and thymol. The antifungal and antibacterial effects of this plant are related to the existence of these substances (Noumi et al., 2010, Al-Bayati and Sulaiman, 2008). The World Health Organisation (WHO) recommends and encourages the use of toothbrushes as an effective tool for dental health care in healthcare settings (Sofrata et al., 2008). Also, one of the promising solutions to overcome bacterial and fungal resistance is the use of nanoemulsion of this plant's essential oil, due to its reduced size of particles and increased surface-to-volume ration (Ghosh et al., 2013). Essential oil derived nanoemulsion is considered as a good antimicrobial compound, whose particle size is 10–1 000 nm (Ghosh et al., 2013). This feature is due to the reduction of particle size and the increase of contact surface of nanoemulsion with microbial agents. Thus, we aimed to investigate the antimicrobial effect of the alcoholic extract, essential oil, and nanoemulsion of the S. persica root on clinically important gram-positive and gram-negative bacteria and fungi.