Molecular analysis of tetracycline resistance in Pasteurella aerogenes

Tetracycline-resistant Pasteurella aerogenes isolates obtained from the int estinal tract of swine were investigated for their let genes by PCR analysi s and hybridization experiments. In contrast to Pasteurella isolates from t he respiratory tract, tet(H) genes were detected in the chromosomal DNA of only 2 of the 24 isolates, one of which also carried two copies of a tet(B) gene. All other P. aerogenes isolates carried tet(B) genes, which are the predominant let genes among Enterobacteriaceae. A single isolate harbored a tet(B) gene as part of a truncated Tn10 element on the 4.8-kb plasmid pPAT 2. Comparative analysis of the pPAT2 sequence suggested that the Tn10 relic on plasmid pPAT2 is the result of several illegitimate recombination event s. The remaining 21 P. aerogenes isolates carried one or two copies of the tet(B) gene in their chromosomal DNA. In the majority of the cases, these t et(B) genes were associated with copies of Tn10 as confirmed by their SfuI and BamHI hybridization patterns. No correlation between the number of let gene copies and the MICs of tetracycline, doxycyline and minocycline was ob served.