Antibacterial and Antifungal Activities of Andrographolide in Combination with Antimicrobial drugs

Abstract

Background and objectives: The resistance of infectious pathogens to antimicrobial drugs is an underestimated threat to public health. This rapidly developing phenomenon necessitates the discovery of new treatment strategies. Combining natural compounds with first-line antimicrobials is one treatment strategy to mitigate the emergence of resistant pathogens. Andrographolide, a diterpene lactone isolated from Andrographis paniculata has been reported to possess potent anti-infective activity. This study was conducted to evaluate the combination effect of andrographolide with first-line antimicrobial drugs to fight emerging resistance. Method: The minimum inhibitory concentration (MIC), fold increase in antimicrobial efficacy and fractional inhibitory concentrations (FIC) of andrographolide and ceftriaxone, ciprofloxacin, amoxicillin, metronidazole, amikacin, clindamycin and fluconazole were determined using the high throughput spot culture growth inhibition (HT-SPOTi) assay against ten isolated clinical strains; Streptococcus pyogenes, Escherichia coli, Vibrio cholerae, Pseudomonas aeruginosa, Staphylococcus aureus, Proteus mirabilis, Klebsiella pneumoniae, Enterococcus faecalis, Salmonella paratyphi B and Candida albicans. Results: Combination of andrographolide and the first-line antimicrobials showed various degrees of susceptibility and efficacy against the tested microorganisms with the highest MIC, 0.85 μg/mL recorded. The FICI (Fractional Inhibitory Concentration Indices) for synergy ranged between 0.00 to 0.28 depending on the microorganism and antimicrobial drug. Conclusion: Use of andrographolide with first-line antimicrobials could aid in combating the menace of resistance pathogens. However, this should be done with caution as some of the antimicrobials tested exhibited antagonistic effects.

Keywords

• andrographolide
• antibacterial activity
• antimicrobial drugs
• high-throughput screen