Self-transmissible multidrug resistance plasmids in Escherichia coli of the normal intestinal flora of healthy swine

The resistance genes and their surroundings on three self-transmissible pla smids found in Escherichia coil of the enteric normal flora of healthy pigs have been characterized. The resistance elements found are similar to thos e commonly found in clinical isolates, like the transposon Tn1721 including the Tet A tetracycline resistance determinant, Tn10 with the Tet B determi nant, Tn21 including a class 1 integron with the aadA1a cassette inserted, sulII encoding sulfonamide resistance, and the strA-strB genes responsible for streptomycin resistance, The plasmids were able to mobilize into variou s recipients, including swine pathogens, zoonotic bacteria, and commensals when conjugation experiments were carried out. Transfer of plasmids did not require optimal conditions concerning nutrition and temperature as plasmid s were transferred in 0.9% saline at room temperature, suggesting that in v ivo transfer might be possible. This study shows that transferable resistan ce elements appearing in normal flora bacteria from animals are similar to those commonly found in clinical isolates of human origin. The results indi cate a probable communication between pathogens and the normal flora with r espect to exchange of resistance factors.