Several mobile genetic elements (transposons, integrons, pathogenicity islands) play important roles in the horizontal transfer of virulence genes of pathogenic bacteria. The prevention and therapy of the disease caused by these bacteria is often hampered by antibiotic resistance of these bacteria that may also be due to horizontal gene transfers. The author's investigations directed to the two farm animal species being under the most intensive antibiotic treatments. They aimed at the PCR detection and typing of tetracycline resistance (tet) genes of Salmonella (S. Hadar and S. Typhimurium) and of E. coli (enterotoxigenic, verotoxigenic, and enteroptahogenic) from swine, as well as of avian E. coli. Furthermore they aimed to investigate the possible genetic links between tetracycline resistance and enterotoxicity in porcine enterotoxigenic E. coli (ETEC). Altogether 43 Salmonella (from Hungary), and 172 E. coli strains (from USA, Austria and Hungary) were tested by using PCR primers for the following tet typing genes: tetA, tetB, tetC, tetD, tetG, believed to be most frequent in these bacteria. As a result, the antibiotic resistance genes of almost all Salmonella and E. coli bacteria have been determined. The tetA gene dominated in the S. Hadar and the Hungarian and Austrian E. coli strains. In contrast, tetB was the most frequently occurring type of tet genes in the the porcine enterotoxigenic, and verotoxigenic E. coli (ETEC, VTEC) from the US. The 5. Typhimurium strains (approx. half of them DT104) contained the tetG gene known to be part of the Salmonella genomic island (SGI), and to be characteristic to DT104 strains. A series of their studies (7, 21) is briefly reviewed here, where the possible genetic links between tetracycline resistance and enterotoxicity in porcine postweaning ETEC the tetB gene was found to be located on a large (approx. 90 kb) virulence plasmid (pTC). Results of sequencing studies indicated that tetB was part of a Tn10 transposone, while the virulence genes (encoding sta, and stb enterotoxins) were localized on a 10 kb toxin specific locus (TSL) of the same plasmid. This TSL was proven to be part of a larger pathogenicity island (PAI). These results indicated that the large virulence plasmid (pTC) of porcine ETEC does not only carry the genes of heat stable enterotoxins (sta, stb), but also carries the gene for tetracycline resistance, thereby being responsible for joint transmission of tetracycline resistance and virulence between bacteria.
|Translated title of the contribution||The role of mobile genetic elements in the horizontal spread of tetracycline resistance and virulence of certain Escherichia coli and Salmonella bacteria|
|Number of pages||9|
|Journal||Magyar Allatorvosok Lapja|
|Publication status||Published - Dec 1 2006|
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