The emergence of antibiotic resistance has prompted scientist to assiduously research into medicinal plants, not only to ascertain claims of efficacy and safety but also to discover alternative candidates for drug development. In the same regard the current study sought to elucidate the antimicrobial activity of ethanolic fractions of Cryptolepis sanguinolenta.
Several studies from the West African sub-region have reported the potency of C
against clinical malaria [4
]. The efficacy of its different alkaloids hydroxycryptolepine, cryptolepine HCl and the corresponding base cryptolepine as antifungal, antimalarial and antibacterial has also been reported [16
High resistance observed in the clinical isolates is consistent with emerging antimicrobial resistance worldwide, especially in developing nations like Ghana [18
]. All bacteria tested were completely resistant to the relatively affordable antibiotics available today; like ampicillin, cloxacillin, tetracycline and penicillin, while observed resistance to gentamicin was below fifty percent. High anti-bacterial resistance to ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracycline in animals and humans has also been reported in Europe and America [20
]. The simultaneous use of antimicrobial agents in both human and veterinary medicines have widened the spectrum of resistance to cover trimethoprim, fluoroquinolones and third-generation cephalosporin [21
]. Even though there are natural ways microbes develop resistance [22
], compliance with pharmaco-vigilance policies will help slow the rate of antibiotic resistance.
The phytochemical analyses revealed the presence of alkaloids, polyuronides and anthocyanosides in the ethanol extract, chloroform and water fractions. However, triterpenes were found only in the water fraction. There are reports on the antimicrobial activities of alkaloids against wide spectra of microbes- according to Cimanga et al
], ethanol-water extract isolation of the alkaloids quindoline, hydroxycryptolepine, cryptolepine-HCl, and the corresponding base cryptolepine was found to inhibit Gram-positive bacteria and some selected Gram-negative bacteria [18
]. Terpenoids are known to have antimicrobial properties [23
]. For instance, triterpenes, terpenoids or isoprenoids, are reported to show high antifungal or antimicrobial properties with possible effect on the non-mevalonate pathway. This pathway is essential in fungi, protozoans, gram-negative bacteria and other micro-organisms for the synthesis of cell membrane components, prenylation of proteins and as a secondary source of carbon [24
]. Reducing sugars have been reported to have antibacterial property [25
]. The petroleum ether acting as a defatting agent removed oils from the extract. This may be a contributing factor to the microbial susceptibility observed since most oils from plants have antimicrobial activity [27
]. The activity of these phytochemical-constituents may be responsible for the antimicrobial activities observed in the study.
The ethanol extract inhibited both Gram positive and Gram negative bacteria with greater inhibition zones observed among the Gram-positive microbes, probably due to difference in cell wall structure and component. This result is consistent with the work of Mills-Robertson et al
]. The inhibition of S. saprophyticus
, E. coli
and P. mirabilis
confirm the use of the plant in the treatment of UTI [28
]. Aqueous and 80% Ethanol-water extract from the root-bark of Cryptolepis sanguinolenta
are known to have potent antibacterial, anti-complementary, and moderate antiviral activities, but not antifungal [18
]. The petroleum ether fraction of the ethanol extract of C. sanguinolenta
inhibited the growth of only the standard Gram-positive bacteria; however, both the standard and wild strains of Proteus mirabilis
were susceptible. C
has been shown to contain alkaloids which function to cause cell lysis and morphological changes in S. aureus
]. The inhibition of only the Gram-positive organisms as well as Proteus mirabilis
by the petroleum ether fraction may suggest the presence of such compounds; hence the fraction may be used as narrow spectrum antimicrobial.
The chloroform fraction registered hundred percent inhibitory activities against all the sixteen isolates. Paulo et al
] investigated the antimicrobial activity of ethanol extract and five alkaloids of C. sanguinolenta
and observed that P. aeruginosa
was resistant to all the alkaloids and the extract. However, this present study observed that the chloroform fraction of C. sanguinolenta
has inhibitory activity against P. aeruginosa
; hence, the fraction may be used in the treatment of infections involving these MDR organisms. The chloroform extracts of Thaumatococcus danielli
leaves have no significant antimicrobial activity against Salmonella typhimurium, Shigella sp, Escherichia coli
and Staphylococcus aureus
]. Moreover chloroform extracts of Centrosema pubescens
inhibited the growth of same organisms [31
], a justification that the inhibition was not caused by chloroform but rather its constituents. It is thought that chloroform has the potential of extracting some potent compounds which are present in minute proportion in the ethanolic extract. In addition, synergism may be a plausible explanation for this observation [32
]. These phenomena requires further investigated.
The ethyl acetate fraction inhibited the growth of three out of the sixteen (18.75%). All the other test microbes (n
13) were not susceptible to the extract. The few organisms inhibited by the fraction could be justified by the dose-dependent activity observed by Cimanga et al
]. Probably the active compounds contained in the fraction were not sufficient to inhibit most of the organisms. The water fraction of C
inhibited twelve out of the sixteen (75.00%) microbes used. The growths of all the Gram-positive microbes were inhibited. Non susceptibility was observed among S. typhi, S. typhimurium, S. typhimurium
(ATCC 14028) and K. pneumoniae
(ATCC 33495). The remaining eight Gram-negative organisms were inhibited by the extract. The aqueous fraction has been reported to have a broad spectrum antimicrobial activity [6
Gram-positive test organisms were generally susceptible to the various fractions used. This may be due to the about 90% peptidoglycan component of the cell wall of Gram-positive bacteria, which is not a regulatory in comparison to the cell membrane of the gram negative bacteria, and therefore, incapable of performing the function of selective permeability, and thus allow substances to sieve through it. The Gram-negative organisms showed varying resistance to all fractions and extract except the chloroform fraction. The Gram-negative bacteria cell wall consist of a peri-plasmic space that contains many hydrolytic enzymes, including β-lactamase, which destroy potentially dangerous foreign substances present in this space.
All the extract and fractions showed MIC values ranging from 0.5
mg/ml to 32
mg/ml but not all were bactericidal. Considering the fact that the chloroform fraction used is a crude extract, the MIC value recorded (0.5
mg/ml) against S. aureus
and a maximum of 4
mg/ml in the other test organisms shows how potent it could be used as an antimicrobial agent. MICs observed in this study are high compared to some studies like Akiyemi et al.
]. They reported the effectiveness of crude extracts of three medicinal plants from Nigeria against MRSA, and observed MICs ranging from 18.2 to 71.0 ug/ml. Another study [36
] determined the antimicrobial activity of three selected plants against Extended Spectrum Beta Lactamase (ESBL)—producing Escherichia coli
and Klebsiella pneumoniae
and found majority of the microorganisms inhibited by 40 and 80μ
l of the crude extracts. However the current MICs observed is consistently justified by similar studies. Navarro et al.
] investigating 12 methanolic plant extracts normally used in traditional medicine in Mexico to cure infectious diseases, examined the potential antimicrobial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa
and Candida albicans.
They reported significant antimicrobial effects, as MICs, ranging between 0.6 and 40
mg/ml of crude extract against the microbes. Another study also reported that Gram-negative bacteria are hardly susceptible to the plant extracts in doses less than 2 × 105