Effects of copper-bearing montmorillonite on Salmonella spp. in vitro study

Abstract

Clay is an important material available in nature. Montmorillonite is considered viable for producing enhanced
performance in a variety of materials and products. Farmed animals such as pigs and poultry receive additional Zn
and Cu in their diets as supplements in their compound feed and these elements are also used for medical remedies.
This study aimed to observe the bactericidal activity of copper-bearing montmorillonite (Cu-MMT) against Salmonella
spp. in vitro. The experiments were divided into two methods that effect Salmonella spp.. First, Cu-MMT was used to
precipitate the Cu2+ ion supernatant mixed with bacteria. The second, Cu-MMT was directly mixed with the bacteria.
The results indicate that the optimal bactericidal concentration of the Cu2+ ion supernatant precipitated by Cu-MMT was
0.1 mg/mL for 24 hours, and the optimal sterilisation concentration of Cu-MMT was directly mixed with Salmonella
spp. at 0.05 mg/mL for 24 hours. When Salmonella spp. was mixed with Cu2+ ion or Cu-MMT, the effects on the cell
types could be clearly discerned with an electron microscope. Scanning electron microscope (SEM) or Transmission
electron microscope (TEM) showed that many bacteria were adsorbed by Cu-MMT. The appearance of the bacteria
exhibited an uneven morphology, the cell wall was ruptured, the cell membrane was broken, the cells appeared as
bubbles and the osmotic pressure of the Cu2+ ion liquid caused the cell wall to separate from the cytoplasm. Here was
an important reason for the antibacterial effect and bactericidal ability of Cu-MMT.