Assessment of herbal drugs for promising anti-Candida activity

Abstract

Background: Microbial infections are diverse and cause serious human diseases. Candida albicans infections are serious healthcare-related infections that are complicated by its morphological switching from yeast to hyphae, resistant biofilm formation and mixed infections with bacteria. Due to the increase in drug resistance to currently used antimicrobial agents and the presence of undesirable side effects, the need for safe and effective novel therapies is important. Compounds derived from plants are known for their medicinal properties including antimicrobial activities. The purpose of the study was to compare and evaluate the anti-Candida activities of several medicinal plants in order for the selection of a herbal drug for human use as effective antimicrobial. The selection was taking into considerations two important parameters; parameters related to the selected drug including activity, stability, solubility and toxicity and parameters related to the pathogen including its different dynamic growth and its accompanied secondary bacterial infections.

Methods: Seven different plants including Avicennia marina (Qurm), Fagonia indica (Shoka'a), Lawsania inermis (Henna), Portulaca oleracea (Baq'lah), Salvadora persica (Souwak), Ziziphus spina- Christi (Sidr) and Asphodelus tenuifolius (Kufer) were ground and extracted with ethanol. The ethanol extracts were evaporated and the residual extract dissolved in water prior to testing against Candida albicans in its different morphologies. The antibacterial and cytotoxic effects of the plants extracts were also tested.

Results: Out of the seven tested plants, L. inermis and P. oleracea showed significant anti-Candida activity with MIC ~10 μg/mL. Furthermore, both plant extracts were able to inhibit C. albicans growth at its dynamic growth phases including biofilm formation and age resistance. Accompanied secondary bacterial infections can complicate Candida pathogenesis. L. inermis and P. oleracea extracts showed effective antibacterial activities against S. aureus, P. aeruginosa, E. coli, and the multidrug resistant (MDR) A. baumannii and Klebsiella pneumoniae. Both extracts showed no toxicity when measured at their MIC on human erythrocytes.

Conclusion: The results from this study suggested that L. inermis and P. oleracea extracts and/or their chemicals are likely to be promising drugs for human use against C. albicans and MDR bacteria.

Keywords: Activity; Antimicrobial; Biofilm; Candida albicans; Medicinal plant; Toxicity.

Fig. 1

Antimicrobial activities of alcoholic plant extracts. a Quantitative microtiter plate assay for biofilm formation using MTT method. The effect of both L. inermis and P. oleracea plants extracts were tested on C. albicans compared to no extract as negative control. b Bacterial growth inhibition by crude alcoholic plant extracts. The effect of alcoholic plant extracts on the growth of E. coli, S. aureus, Acinetobacter baumanii, Klebsiella pneumoniae, and Pseudomonas aeruginosa was tested in 24-well micro-plates. c Influence of L. inermis and P. oleracea alcoholic extracts on 24 h-grwoing C. albicans in batch culture. The graph represents the re-inoculation of either alcoholic plant extracts-treated Candida or untreated cultures into fresh antibiotic-free media followed by incubation at 37 °C for 24 h. The data was analyzed using one-way analysis of variance (ANOVA) using Dunnett’s Multiple Comparison Test. P value < 0.05 was considered as significant. The standard error represents the mean of three replicas

Fig. 2

Dose-dependent hemolytic activity of alcoholic plant extracts to human erythrocytes. DPBS-washed erythrocytes (3 × 10⁶ cells per well) were incubated in 96-well plate with the total plant extracts at different concentrations (ranging from 3.6 to 100 μg/mL) at 37 °C for 30 min. The hemoglobin released from lysed erythrocytes was measured using micro-plate reader at 405 nm. The absorbance values for each sample were subtracted from the absorbance value of cells treated only with washing buffer and the hemolytic activity (%) was calculated. The experiment was conducted in triplicate