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Abstract
The plasmid pBR322 contains the genes bla and tetA, which encode resistance to ampicillin and tetracycline. Escherichia coli DH5 α cells containing pBR322 were grown in concentrations of 50, 100, 150 and 200 µg/ml of ampicillin or 10, 15, 30 and 45 µg/ml of tetracycline. The cells were lysed and their proteins separated into cytosolic, periplasmic, membrane and secreted fractions. SDS-PAGE was carried out on the isolated fractions and the band intensities of 31 kDa and 46 kDa proteins (corresponding to the bla and tetA gene products respectively) were analyzed. It was found that both bla and tetA have basal levels of expression, which increase in response to the antibiotics to which they encode resistance – although not necessarily in a linear fashion. In addition, it was discovered that membrane stability and membrane potential also play important roles in how resistance proteins from pBR322 are expressed in response to antibiotic treatment.