Identification of a truncated, but functionally active tet(H) tetracyclineresistance gene in Pasteurella aerogenes and Pasteurella multocida

Molecular analysis of Pasteurella isolates of animal origin for plasmid-enc oded tetracycline resistance genes identified a common tet(H)-carrying plas mid of 5.5 kbp in a single isolate of Pasteurella aerogenes and six isolate s of Pasteurella multocida. This plasmid carried a truncated Tn5706 element in which one of the IS elements, IS1596, was lost completely and of the ot her, IS1597, only a relic of 84 bp was left. Sequencing of the resistance g ene region and the flanking areas revealed the presence of a deletion in th e 3' end of the tet(H) gene which shortened the tet(H) reading frame by 24 bp. The amino acid sequence of the respective TetH protein comprised only 3 92 amino acids. Despite this deletion, the tet(H) gene conferred high level tetracycline resistance not only to the original Pasteurella isolates but also to the respective Escherichia coli JM107 and C600 transformants as con firmed by MIC determination. The deletion was probably the result from reco mbinational events. Two possible recombination sites involved in the deleti on of tet(H) and that of IS1597 were identified. Macrorestriction analysis of the Pasteurella isolates carrying plasmid pPAT1 confirmed horizontal and vertical transfer of this plasmid. (C) 2000 Federation of European Microbi ological Societies. Published by Elsevier Science B.V. All rights reserved.