Detection of a plasmid containing Cadmium resistance gene for lactic acid bacteria isolated from foods

This study aimed to isolate lactic acid bacteria (LAB) carrying cadmium resistant genes on plasmids from foods. A total of 30 fermented food samples were collected from local markets and supermarkets. Isolation of cadmium resistant LAB colonies was performed by spread plate technique using MRS agar medium supplemented with cadmium (MRS-Cd). One hundred and fifty cadmium resistant isolates were randomly selected and subjected to plasmid extraction. Only one isolate (LAB-V12) from a fermented vegetable harbored a single plasmid of about 9 Kb. 16S rDNA sequencing data showed that LAB-V12 was likely to be Lactobacillus plantarum. The results from plasmid curing demonstrated that a cured strain of the LAB-V12 was sensitive to cadmium. Hence, probably cadmium resistant marker is plasmid mediated. The plasmid containing cadmium resistance gene was tested for stability in its host. It was observed that the LAB-V12 could maintain the plasmid after approximately 100 generations of growth without cadmium selection. The plasmid might be further developed to be a food-grade cloning vector that is useful for genetic modification of LAB.