The ultrastructural damage caused by Eugenia zeyheri and Syzygium legatii acetone leaf extracts on pathogenic Escherichia coli

Ibukun M Famuyide,Folorunso O Fasina,Lyndy J Mcgaw,Jacobus N Eloff

doi:10.1186/s12917-020-02547-5

Abstract

BackgroundAntibiotics are commonly added to livestock feeds in sub-therapeutic doses as growth promoters and for prophylaxis against pathogenic microbes, especially those implicated in diarrhoea. While this practice has improved livestock production, it is a major cause of antimicrobial resistance in microbes affecting livestock and humans. This has led to the banning of prophylactic antibiotic use in animals in many countries. To compensate for this, alternatives have been sought from natural sources such as plants. While many studies have reported the antimicrobial activity of medicinal plants with potential for use as phytogenic/botanical feed additives, little information exists on their mode of action. This study is based on our earlier work and describes ultrastructural damage induced by acetone crude leaf extracts of Syzygium legatii and Eugenia zeyheri (Myrtaceae) active against diarrhoeagenic E. coli of swine origin using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescent microscopy (FM). Gas chromatography/mass spectrometry (GC-MS) was used to investigate the chemical composition of plant extracts.ResultsThe extracts damaged the internal and external anatomy of the cytoplasmic membrane and inner structure at a concentration of 0.04 mg/mL. Extracts also led to an increased influx of propidium iodide into treated bacterial cells suggesting compromised cellular integrity and cellular damage. Non-polar compounds such as α-amyrin, friedelan-3-one, lupeol, and β-sitosterol were abundant in the extracts.ConclusionsThe extracts of S. legatii and E. zeyheri caused ultrastructural damage to E. coli cells characterized by altered external and internal morphology. These observations may assist in elucidating the mode of action of the extracts.

Highlights

Antibiotics are commonly added to livestock feeds in sub-therapeutic doses as growth promoters and for prophylaxis against pathogenic microbes, especially those implicated in diarrhoea
This study described the morphological and ultrastructural alterations caused by crude acetone extracts of S. legatii and E. zeyheri on a diarrhoeagenic E. coli strain of swine origin, using scanning and transmission electron microscopy
Some cells had chromatin condensation which was packed into apoptotic-like bodies (e.g. Figure 3d, e; Fig. 4e, f) while the membrane of some cells was detached from the cell wall with electron sparse cytoplasm (e.g. Figure 4c, and d)

Summary

Introduction

Antibiotics are commonly added to livestock feeds in sub-therapeutic doses as growth promoters and for prophylaxis against pathogenic microbes, especially those implicated in diarrhoea While this practice has improved livestock production, it is a major cause of antimicrobial resistance in microbes affecting livestock and humans. Due to the strong association between antibiotic resistance and the use of antimicrobials in livestock, especially as feed additives, some countries in the European Union have banned use of antibiotics as growth promoters [3] This has motivated the search for suitable alternatives including the use of standardized plant extracts or isolated compounds. Scanning and transmission electron microscopy aid the visualization of images at high resolution, providing detailed information on normal or abnormal external and internal cellular morphology such as the cell membrane, cytoplasm, nucleus, organelles and cytoskeletal structures [8, 9]. These methods have greater advantages over conventional light microscopy because they are able to give three-dimensional images and higher image resolutions compared to light microscopy [10]

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Conclusion