Submitted to: American Society for Microbiology Meeting
Publication Type: Abstract only
Publication Acceptance Date: 4/20/2001
Publication Date: 5/20/2001
Citation: Maurer, J.J., Dasher, L., Jackson, C.R., Wooley, R.E. 2001. Physical linkage of multiple drug resistance transposon tn21 to colicin plasmids and disinfectant resistance gene merb in avian escherichia coli. American Society for Microbiology Meeting. Session Number. 263/Z. Abstract. Z-55. P. 750. Interpretive Summary:
Technical Abstract: Recently, we have reported on the widespread distribution of multiple-drug resistance transposon, Tn21 among clinical, avian Escherichia coli isolates in North Georgia. Tn21 is a 21 kb transposon that contains an integron, a mobile genetic element that “captures” antibiotic resistance gene(s), streptomycin, spectinomycin-streptomycin resistance gene aadA1, and inorganic mercury resistance operon mer. It is currently uncertain what selective advantage the organism may gain from mercury resistance since mercury compounds are not used in hatchery disinfectants. The transposon also encodes resistances to antibiotics that are no longer prescribed, while it continues to persist in E. coli without the selection pressure to perpetuate it. Since MerA mercury reductase does not confer cross-resistance to other heavy metals, the selection pressure is probably not due to arsenic compounds added to poultry feed. An ancillary gene merB, present in some mercury resistance operons, does confer resistance to organic mercurials. The widespread distribution of the transposon, Tn21 among clinical isolates is possibly attributed to the conjugative plasmids on which they reside. Seventy-two percent of avian E. coli isolates contain colicin-producing plasmids. Fifty-percent of E. coli isolates examined also contained merB, the organic mercurial lyase. Linkage of the transposon to these plasmids, might explain the persistence of this genetic element. We found physical linkage between Tn21 and colicin genes as well as the association of the organic mercury resistance gene merB with multiple-drug resistant, avian E coli, factors which explain persistence of resistance to drugs no longer used in veterinary medicine.