Final answer:
The resistance factor against tetracycline involves mechanisms like the ykkCD toxin sensor in bacteria, which upon detecting tetracycline, induces protective responses such as activating efflux pumps to remove the antibiotic, thus allowing the bacteria to resist its therapeutic effects.
Step-by-step explanation:
The resistance factor against tetracycline refers to the ability of bacteria to withstand the effects of the antibiotic tetracycline. One mechanism of resistance is the presence of the ykkCD toxin sensor and the associated multidrug-resistant efflux pump found in Bacillus subtilis. For instance, plasmids such as pBR322, used in genetic engineering and research, can carry genes that confer resistance to ampicillin and tetracycline. When these genes are present, E. coli cells which are normally sensitive to the antibiotics can survive in mediums containing these drugs. The ykkCD sensor detects the presence of tetracycline and induces a structural change in mRNA which then promotes transcription and translation of the efflux pump gene. The efflux pump actively removes tetracycline from the cell, thus rendering the antibiotic ineffective and allowing the bacteria to survive even in the presence of tetracycline.