Antimicrobial resistance of three common molecularly identified pathogenic bacteria to Allium aqueous extracts

Highlights

• Antibacterial activity of Allium sp. extracts was assayed.

• Aqueous extract of white garlic had the best antibacterial activity at 0.25 g/mL.

• Black garlic extract had no antimicrobial action on the pathogenic bacteria.

• Extracts can be used as alternatives to replace synthetic antimicrobials.

Abstract

The aim of this work was to evaluate the in vitro bacterial inhibition of different types of garlic on Escherichia coli ATCC 25922, Listeria monocytogenes and Staphylococcus aureus. The bacterial strains were molecularly identified using gen 16S rDNA molecular identification. Four different types of garlics were used: 1) white, 2) Japanese, 3) elephant and 3) black, and these were evaluated at two different concentrations (0.25 and 0.125 g/mL) per garlic type. Bioactive compounds present in the garlics were identified using high-performance liquid chromatography coupled to ultraviolet detector (HPLC-UV), and total polyphenols were quantified by the Folin-Ciocalteu technique. The Kirby-Bauber method was used for the bacterial evaluation. Aqueous extract of black garlic had the highest amount of polyphenols 6.26 ± 0.21 mg GAE/mL. The area of inhibition was measured and classified as sensitive, intermediate or resistant. Using the disc diffusion assay, higher concentration (0.25 g/mL) of aqueous extract of white garlic had the highest antibacterial activity area, with 21.46 ± 3.94 mm for L. monocytogenes, 20.61 ± 2.47 mm for S. aureus and 17.83 ± 2.21 mm for E. coli. White garlic had comparable antimicrobial activity as the control (tetracycline at 30 μg) as indicated by the size of the inhibition halos. Based on your results, white garlic can be used as an alternative to synthetic antimicrobials.

Introduction

Previously, natural products were used to combat diseases, however, with the discovery of synthetic antibiotics, they were gradually replaced [1,52,53]. Natural products used to be the major ingredient of many drugs but pharmaceutical companies have decreased or even eliminated research on natural products [2,[42], [43], [44], [45], [46],52]. The focus has been on synthetic antibiotics and their indiscriminate use have reduced their effectiveness against infectious diseases in addition to incidences of antibiotics resistance [3,[47], [48], [49], [50]]. Foodborne diseases are still a public health problem worldwide and the causal agents are mainly Escherichia coli O157: H7, Salmonella spp., Listeria monocytogenes, and Clostridium botulinum [4,5]. Bacteria have the ability to adapt to an environment and develop resistance mechanisms, which can be of natural or acquired origin [6,7,51].

Due to the current problems of antibiotics resistance facing the livestock industry, natural products can be viable and economical alternatives [55,57,63]. One of such natural products is garlic (Allium sativum) and there is documented literature on its antibacterial effect [8,9]. Therefore, there is a need to look for new medicines of herbal origin as they cannot contribute to antibiotics resistance and they have little or no toxic effect on livestock [10,57,64]. Garlic (Allium sativum) is an antimicrobial characterized by its high content of sulfuric compounds [11,12,54] and previous studies reported that garlic has a broad spectrum of antibacterial activity against E. coli, Salmonella spp. [9,13]. Kamra et al. [14] reported garlic as anti-methanogenic and anti-protozoal agent with the ability to reduce methane emission. They concluded that garlic and plant extract, in general, can be used as an eco-friendly rumen modifier for sustainable production [15,[56], [57], [58], [59], [60], [61], [62]]. During processing, the unstable compounds of fresh garlic, including alliin, become stable compounds that include s-allylcysteine (SAC), the water-soluble compound with potent antioxidant effect [16]. The study of medicinal plants is still a work in progress but it has the potential to address some of the major issues such as the antibiotics resistance that have plagued the livestock industry. In the present study, we evaluated two concentrations (0.25 and 0.125 g/mL) of aqueous extracts of white, Japanese, elephant and black garlic for their antibacterial activities on E. coli, L. monocytogenes and Staphylococcus aeurus.