In Vitro Antibacterial Activity of Sweet Basil AgainstEscherichia coli O157H7 Analyzed Using TEM

Abstract

Escherichia coli O157: H7 is a known pathogen responsible for several outbreaks and cases of life-threatening hemorrhagic colitis and hemolytic uremic syndrome. Based on our previous results reported on the activity of basil oil against the pathogen, the oil was bacteriostatic and bactericidal at 0.25 and 0.5 mg/ml, respectively. Therefore, these two concentrations were used in this study to observe their effects on the pathogen under a transmission electron microscope. Stationary phase E. coli O157: H7 cells were treated with the oil. Untreated E. coli O157: H7 was used as a control. A standard procedure for preparing electron microscopy samples was followed.Transmission electron microscope (TEM) images showed that E. coli O157: H7 control cells were rod-shaped and had cellular integrity. The treated cells showed clear ultrastructural damage. When the cells were treated with the 0.25 mg/ml oil, the cell membrane was separated from the cell wall and the cell size was reduced. In addition, irregular shape of the treated cells was also detected. During this time, significant damage was found in cells treated with 0.5 mg/ml oil when cell integrity was completely lost and leakage of cell contents was also observed.