The burden of infectious diseases remains a significant threat to health, especially in developing countries. Infections affect a large proportion of the world population. For example, about 55 million people have a urinary tract infection at any given time [1]. Approximately 357 million people get sexually transmitted infections annually [2]. Respiratory, gastrointestinal, and wound infections, as well as bacteremia and sepsis, are also a significant cause of morbidity disability, and mortality.
Infectious diseases are still a substantial problem despite the rapidly increasing use of antibiotics. Between 2000 and 2020, the defined daily doses (DDD) of antibiotics consumed globally increased from 21.1 billion to 34.8 billion, which translates to a 65% increase [3]. The high rates of use of antibiotics are causing the emergence of antibiotic-resistant bacteria. Besides, synthetic antibiotics are associated with several negative features such as short half-life in vivo, toxicity, and high cost of synthesis [4].
There is a need to reduce the use of antibiotics in response to the problem of antimicrobial resistance (AMR) so that the currently available antibiotics stock may not get depleted [5]. Plant-based botanicals are a viable alternative to antibiotics in efforts to address AMR [6]. Their antimicrobial and chemosensitizer effects can be leveraged to optimize the use of the available antibiotics while reducing the pressure on them [7]. Investigating plants used in traditional medicine to treat infectious diseases for antimicrobial effects can provide evidence of their value in managing infectious diseases.
The varieties of C. edulis in Yemen, South Africa, Saudi Arabia, and Lebanon have been shown to have antibiotic effects against various bacteria in in-vitro studies [8-12]. Fatima et al. [8] tested methanol, dimethyl sulfoxide (DMSO), and water extracts of Catha edulis Forsk in Saudi Arabia against Staphylococcus aureus, Streptococcus pyogenes, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, and Candida albicans clinical isolates. The methanol and DMSO extracts had significant zones of inhibition in all the bacteria tested while the aqueous extract was only active against gram positive organisms, particularly Staphylococcus aureus [8]
Siddiqui [11] tested methanolic crude extracts of C. edulis purchased from a shop in London against various laboratory-stocked microbes (Escherichia coli, Bacillus magaterium, Brevundimonas diminuta, and Micrococcus luteus) using the antibiotic disc diffusion assay. The researcher established that the extracts had significant (breakpoint of 14 mm) antimicrobial effect against all the bacteria tested (zones of inhibition >16 mm for B. magaterium; >19mm for M. luteus) except E. coli (zone of inhibition <11 mm) [11]. The variation in E. coli results in the studies by Fatima et al. [8] and Siddiqui [11] imply that Catha edulis grown in different geographical areas could be having varying antimicrobial effects.
Al-hebshi, Al-haroni, and Skaug [9] evaluated the antimicrobial effect of aqueous extracts of Yemen’s C. edulis against organisms comprising oral microbiota. The extracts showed more effect on the gram-negative bacteria (Porphyromonas gingivalis, Fusobacterium nucleatum, and Prevotella intermedia), which are mainly pathogenic in the mouth, compared to the gram-positive bacteria (Streptococci and Actinomyces), which are mostly the normal flora of the oral cavity [9]. Therefore, Catha edulis could be selectively active against pathogens by sparing normal flora.
Miraa, the common name for Catha edulis varieties cultivated in the Igembe region of Meru County in Kenya, is one of the plants used to treat infectious diseases in traditional medicine. Miraa plant is a dicotyledonous shrub in the Celastraceae family whose twigs are harvested and commonly chewed for recreational purposes [13]. There are C. edulis varieties in other parts of the world including Yemen, Ethiopia, Saudi Arabia, South Africa, and Lebanon. According to an ethnobiology study by Kiunga et al.[14], herbalists in Meru use decoctions of the leaves and roots of Miraa to treat oral, respiratory, diarrheal, and urogenital diseases. Miraa can be a suitable source of plant-based botanicals if its antimicrobial properties are established. Its availability is assured given that it is a cultivatable plant without scarcity challenges faced when wild plants are used as sources [15].
The illnesses that herbalists treat using Miraa could be caused by myriad pathogens. S. aureus is a common cause of respiratory, urinary tract, and gastrointestinal infections [16], which herbalists apply Miraa decoctions to treat. Methicillin-resistant S. aureus (MRSA) is rapidly spreading globally amidst the reducing antibiotic options to treat its infections [17]. Streptococcus pyogenes is a common cause of sore throat, one of the respiratory infections that herbalists treat using Miraa decoctions. Its infections have increased in the last three decades and it is commonly developing resistance to antibiotics [18]. Streptococcus pneumoniae, which causes respiratory infections, is a pathogen against which antibiotic resistance is rapidly emerging due to antibiotic selection pressure [19]. Escherichia coli is a common cause of urinary tract, gastrointestinal, and respiratory infections; it is common in outbreaks [20]. Hence, E. coli is a suitable representative of gram-negative bacteria in studies to identify plants that can be sources of antimicrobial botanicals. Candida albicans is a fungus that causes oropharyngeal and vulvovaginal candidiasis. Its multi-drug resistant strains are rapidly emerging. Thus, it is an appropriate representative of pathogenic fungi in this study [21].
Our comprehensive review of the literature did not find any study investigating the antimicrobial properties of Miraa, the C. edulis cultivated in Kenya. Studying Miraa to determine its antimicrobial effects was essential to generate information on whether it has antimicrobial effects like the varieties tested in other countries. This article reports the in-vitro antimicrobial effects of aqueous and methanolic crude Miraa extracts against Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, and Candida albicans clinical isolates, and Streptococcus pyogenes ATCC 19615 and methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300 standard strains.