Abstract
The resistance genes and their surroundings on three self-transmissible plasmids found in
Escherichia coli
of the enteric normal flora of healthy pigs have been characterized. The resistance elements
found are similar to those commonly found in clinical isolates, like the transposon Tn
1721
including the Tet A tetracycline resistance determinant, Tn
10
with the Tet B determinant, Tn
21
including a class 1 integron with the
aadA1a
cassette inserted,
sulII
encoding sulfonamide resistance, and the
str
A-
str
B genes responsible for streptomycin resistance. The plasmids
were able to mobilize into various 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 plasmids were transferred in 0.9% saline at room temperature, suggesting that
in vivo
transfer might be possible. This study shows that transferable resistance
elements appearing in normal flora bacteria from animals are similar to those commonly found in clinical isolates of human origin. The results indicate a probable communication between pathogens and the
normal flora with respect to exchange of resistance factors.