Bertrand, Kevin P.
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Research Interests
Tetracycline resistance in Gram-negative bacteria such as Escherichia coli is mediated by a plasmid-encoded membrane protein (TetA) that pumps the antibiotic out of the cell. Sequence data suggest that TetA is a member of a large family of bacterial and animal cell transport proteins that share a common structure. We are using gene fusion and site-directed mutagenesis techniques to study the structure and function of TetA and the mechanism of its insertion into the cell membrane.
Gram-negative bacteria are intrinsically resistant to a large group of hydrophobic compounds that includes dyes and detergents as well as many antibiotics. Recent work suggests that E. coli possesses a family of broad-specificity efflux pumps that act to reduce the intracellular concentration of these structurally unrelated compounds. The E. coli acrAB operon encodes two membrane proteins that are both necessary for resistance to hydrophobic compounds. However, mutations that increase expression of a second operon, acrEF, can compensate for mutations in acrAB. Based on their sequences, the acrAB and acrEF operons encode homologous pairs of proteins. In addition, the AcrB and AcrF proteins are homologous to two metal efflux proteins from another species of bacteria. These sequence comparisons, together with transport studies on acrA mutants, suggest that the AcrAB and AcrEF proteins also function as efflux systems. We are using a combination of genetic and biochemical techniques to study the structure, function, and regulation of AcrAB and AcrEF.

Publications
Allard, J. D., and K. P. Bertrand, 1992. Membrane topology of the pBR322 tetracycline resistance protein: tetA-phoA gene fusions and implications for the mechanism of TetA membrane insertion. J. Biol. Chem. 267:17809-17819.

Allard, J. D., and K. P. Bertrand, 1993. Sequence of a Class E tetracycline resistance gene from Escherichia coli and comparison of related tetracycline efflux proteins. J. Bacterio. 175:4554-4560.

Rothstein, D. M., M. McGlynn, V. Bernan, J. McGahren, J. Zaccardi, N. Cekleniak, and K. P. Bertrand, 1993. Detection of tetracyclines and efflux pump inhibitors. Antimicrob. Agents Chemother. 37:1624-1629.