Assessing the combinations of 'old' Polymyxin drug and medicinal plant extracts in combating gram-negative bacteria towards development of Halal and Toyyib antibiotics

Abstract

A rapid increase of bacterial resistance particularly Gram-negative bacteria is a major threat to human health as many standard antibiotics have become less effective in treating infectious diseases. With the fairly dry discovery and development pipeline of novel drugs, it is very unlikely to obtain new drugs in the near future. Polymyxins, an ‘old’ antibiotic class, has been revived as the last-line therapeutic arsenal for infections caused by multidrug-resistant (MDR) Gram-negative bacteria. Nevertheless, its application in clinical practice was restrained due to a number of nephrotoxicity and neurotoxicity cases reported. Plant-based therapy has been considered safe, effective and has been promisingly integrated with modern medicine. Combination therapy is a potential approach in the fight against Gram-negative bacteria or ‘superbugs’ which comply with the toyyiban viewpoint in Halal pharmaceutical. Toyyib is an important aspect to ensure that the medicines must be non-hazardous, non-intoxicating, and safe for clinical practice according to the prescribed dosage. This study sought to investigate the effect of local medicinal plant extracts in combination with polymyxin B against Gram-negative bacteria. Selected plants such as Annona muricata, Andrographis paniculate, Piper sarmentosum, Clinacanthus nutans and Aquilaria malaccensis which are known for their antimicrobial property were extracted by soxhlet method. The crude ethanolic extracts were screened for their antibacterial activity and assessed for their killing activity in combination with polymyxin B against Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae. The selected extract was analyzed for their chemical constituents using Gas chromatography-mass spectrometry (GC-MS). The study revealed that, throughout ten plants that have been tested, only five plants possessed an antibacterial activity, with the highest was A. malaccensis leaves against A. baumannii ATCC 19606 and K. pneumoniae ATCC 10031. The combination of A. malaccensis extract (64 mg/mL) and polymyxin B (1 mg/L) was found to be able to inhibit the bacteria growth and exhibit a better bacterial killing compared to polymyxin B alone. A. malaccensis extract at 64 mg/mL also showed a bactericidal effect with a reduction of ≥ 3 log10 CFU/mL below the initial inoculum at 24 h against both A. baumannii and K. pneumoniae isolates. GC-MS analysis identified phytol, 9,12-octadecadienal, oleic acid, n-hexadecanoic acid, squalene which likely correlated to the antibacterial activity observed from the extract. The results highlighted the potential of polymyxin B and A. malaccensis extract combination to be further leveraged for the treatment against MDR Gram-negative bacteria. In addition, A. malaccensis extract is importantly a subject of potential antibiotic to be explored and developed.