Effects of tetM gene instability on resistance expression in Lactobacillus casei

Lactobacillus casei is one of the probiotic bacteria which has an antibiotic (tetracycline) resistance encoded by tetM gene. This gene can be unstable which leads to the changes of the DNA sequence (mutation) during the adaptation process under a sub-lethal dose of tetracycline antibiotic. The aim of the study is to observe the resistance level and genetic instability of tetM gene under a sub-lethal dose of tetracycline antibiotic and to examine the effect of gene instability on the antibiotic resistance level of L. casei. This study was conducted by 2 steps i.e. determination of sub-lethal dose of L. casei and isolation of L. casei with the highest resistance to tetracycline using adaptation process. This study confirmed that L. casei could survive with sub-lethal dose of 10-50 μg/mL tetracycline and has a lethal dose at 60 μg/mL. The concentration of more than 60 μg/mL tetracycline caused instability of tetM gene and lead to the survival of L. casei at 70 μg/mL tetracycline after adaptation process.