Bacterial strains resistant to arsenical compounds were isolated. Plas
mids with molecular masses from 2.4 to 87 MDa were revealed in nine st
rains. Two conjugative plasmids, pBK1 and pBK2, determined resistance
to arsenical compounds and multiple drug resistance in strains Klebsie
lla pneumoniae 3-129 and Enterobacter aerogenes 3-28, respectively. Th
e genetic determinants of arsenical resistance contained in plasmids p
BK1 and pBK2 can be expressed in Escherichia coli cells, but with lowe
r efficiency than in the donor strains.