Infectious diseases became a re-emerging contemporary global threat to human health with millions of infections and thousands of annual deaths due to antimicrobial resistance (AMR)[1]. AMR is growing at a faster pace than either discovery of new drugs or alternative approaches to tackle it, leaving common infections untreatable [2]. With this resurgence worldwide, the search for novel antimicrobials and alternative approaches to tackle the problem is urgently needed. Modification of existing antibiotics, rediscovering antimicrobials, repurposing antimicrobials, combination treatment, looking for untested sources of antibiotics, and searching for compounds found from chemists around the world are the possible sources of novel antibiotic discovery [3]. Plant based molecules have promising potential for the discovery of novel antimicrobials or as adjuvants in modifying existing antimicrobials [4, 5].
Among the many secondary plant metabolites, essential oils of different plant sources showed noteworthy antibacterial activity [6, 7] and resistance modulatory effect [8]. The antibacterial activities of EO are mainly attributed to the disruption of membrane enhancing the antibacterial activity of combined antibiotics by increasing their influx [9]. This could contribute significant potential in battling AMR as one of the main contributing factors to the increased resistance in bacteria is the permeability barrier caused by their additional outer membrane [3]. The EOs will infringe the outer membrane barrier restoring the activity of antibiotics. This has led to the exploration of antibiotics-EO combinations in battling the antimicrobial resistance. Studies on antibiotics-EOs combinations from various plant sources have shown synergistic activities [9]. Recently, there is renewed research focused in discovering potential novel antibacterial agents and/adjuvants from plant Eos [5].
Echinops kebericho (Asteraceae) is an endemic medicinal plant which is used for the treatment of various diseases [10]. Ethnomedicinal uses of E. kebericho have been recorded for human and livestock ailments. Reported ailments treated by E. kebericho include wound infections, toothache tonsillitis, stomachache, gonorrhea, respiratory manifestations, febrile illness, lung tuberculosis, trypanosmiasis, typhoid, tonsilitis, tooth ache, typhus, common cold, cancer, hypertension, colic, cough, and malaria [11–17]. It is also used to treat scabies, headache, cough, fumigation during childbirth, and mosquito repellent [12]. It is formulated as a water decoction, infusion, smoke inhaled, orally chewed, and topical sprayed to affected area [13, 15–17]. Echinops kebericho was also reported to be used in veterinary practice where root tubers are powdered and mixed with water and given for black leg disease, respiratory manifestations, liver disease, and skin infections [18]. Previous studies revealed flavonoids, alkaloids, triterpenoids, resines, saponins and steroids [19, 20] as components and dehydrocostuslactone is also identified [20–23].
The extracts of E. kebericho exhibited a wide range of pharmacological effects including anti-helminthic, antibacterial, antifungal, antidiarrheal, anti-spasmolytic and antimalarial activities. The methanolic root extract and EO showed relatively strong effect [24, 25] which established a scientific basis for therapeutic uses of E. kebericho. In vitro and in vivo studies have confirmed the ethnomedicinal use [19, 26–28]. Antibacterial activities from crude extracts [24, 29, 30] and EOs [25] were reported. Ivan reported anti-mycobacterium activity against Mycobacterium smegmatis and significant antimicrobial resistance modulatory effects [22]. Significant activities were reported against fungi (Aspergillus flavus and Candida albicans) [24], malaria parasite (Plasmodium berghei) [19], Leishmania [26], earthworm [31], and Trypanosoma [32]. Echinops kebericho extract produced a dose dependent reduction in intestinal propulsion and mean defecation comparable to loperamide [27] and EO produced dose-dependent mosquito repellent activity [33] and moderate larvicidal activity [34]. .
However, the antibacterial activity to different multi-drug-resistant strains and various solvent fractions have not yet been studied. The spectrum of activity and most active component of the extract were not elucidated. Herein, we have determined the antibacterial activity of essential oils and fractions of crude extract to eight strains belonging to five species of bacteria aimed at determining the spectrum of activity and identifying most susceptible strains and paving a way for isolation of most active components against most susceptible strains.