Submitted to: Antimicrobial Agents and Chemotherapy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/8/2004
Publication Date: 3/20/2005
Citation: Stanton, T.B., Humphrey, S.B., Scott, K.P., Flint, H.J. 2005. Hybrid tet genes and tet gene nonmenclature - request for opinion. Antimicrobial Agents and Chemotherapy. 49(3):1265-1266. Interpretive Summary: We analyzed the sequences of genes that make the bacterium Megasphaera elsdenii resistant to the antibiotic tetracycline. This anaerobic bacterium lives in the intestinal tracts of cattle, of swine, and of various other mammals, including humans. These genes are unique because they are composed of pieces of previously known genes. Therefore they are "hybrid" genes. In this paper we used computer programs to analyze the sequences of tetracycline resistance genes from other bacteria. We found that there are other intestinal bacteria with different hybrid tetracycline resistance genes. All of these hybrid genes were not previously known. For this reason, the guidelines for naming hybrid tetracycline resistance genes have not been established. We propose new ways of naming these hybrid genes.
Technical Abstract: The naming of tetracycline resistance genes is currently based on the predicted amino acid sequences of proteins encoded by those genes. Amino acid identity of less than or equal to 80% is the cutoff for defining new determinants. This cutoff value was established for previously known tet genes varying in sequence over their entire lengths and before the discovery of hybrid tet genes. Based on the 80% cutoff, the tet(32) gene, encoding a protein sharing 78.4% amino acid sequence identity with C. jejuni Tet (O), was assigned to a new tet class. A re-evaluation of the tet(32) sequence in this study, however, has led us to conclude that this gene is a mosaic gene formed between tet(O) and an unknown tet gene. Also based on this criterion, three M. elsdenii genes would be designated tet(W) genes, since their translated proteins share, respectively, 95.8%, 89.2%, and 92% identity with the Tet (W) protein of Butyrivibrio fibrisolvens (GenBank AJ222769). However, these genes result from genetic recombination among tet(O) and tet(W) class genes. Current classification guidelines do not adequately reflect the evolutionary position of mosaic genes nor convey their unique recombinant nature. Consequently, we propose that guidelines for naming tet genes be expanded to recognize hybrid tet genes.