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Applied and Environmental Microbiology, December 2005, p. 7941-7947, Vol. 71, No. 12
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.12.7941-7947.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Danish Institute for Food and Veterinary Research, 1790 Copenhagen V, Denmark,1 Statens Serum Institute, 2300 Copenhagen S, Denmark2
Received 2 March 2005/ Accepted 24 August 2005
The presence of tetracycline resistance (Tcr) genes and class I integrons (in-1), and their ability to cotransfer were investigated in Tcr gram-negative (185 strains) and gram-positive (72 strains) bacteria from Danish farmland and pigsties. The isolates belonged to the groups or species Escherichia coli, Enterobacter spp., Arthrobacter spp., Alcaligenes spp., Pseudomonas spp., and Corynebacterium glutamicum. The 257 isolates were screened for in-1. Eighty-one of the gram-negative isolates were also screened for the Tcr genes tet(A), tet(B), and tet(C), and all (n = 72) gram-positive isolates were screened for tet(33). Fourteen (7%) of the soil isolates and eleven (25%) of the pigsty isolates contained in-1. All isolates that contained tet genes also contained in-1, except one gram-negative isolate from a pigsty that contained tet(B). All gram-positive isolates with in-1 also contained tet(33). No isolates contained more than one tet gene. The in-1-positive isolates were tested for resistance to selected antimicrobial agents and showed resistance to three to nine drugs. Filter-mating experiments showed cotransfer of Tcr and class I integrons from soil isolates to Escherichia coli and/or Pseudomonas putida. We conclude that soil bacteria in close contact to manure or pigsty environment may thus have an important role in horizontal spread of resistance. Use of tetracyclines in food animal production may increase not only Tcr but also multidrug resistance (caused by the presence tet genes and in-1) in bacteria.
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