Analysis of pVU3695, a plasmid encoding glutathione-dependent formaldehyde dehydrogenase activity and formaldehyde resistance in the Escherichia coli VU3695 clinical strain.

The formaldehyde resistance of Escherichia coli VU3695 is due to the expression of glutathione-dependent formaldehyde dehydrogenase (GSH-FDH) activity, which is encoded by the adhC gene located on the plasmid pVU3695. Conjugation of this plasmid to an unrelated PolA deficient strain of E. coli indicated that it encodes its own replication initiation protein and does not confer resistance to several other antimicrobial agents tested in this work. In addition, pVU3695 has homology with replicons that belong to the IncL/M plasmid incompatibility group, which are widely distributed among the Enterobacteriaceae. Curing of pVU3695 abolished the expression of formaldehyde resistance and the presence of a 46-kDa periplasmic protein immunologically related to GSH-FDH. However, the curing of pVU3695 reduced drastically but did not abolish the expression of a protein with similar electrophoretic motility, which was associated with the expression of GSH-FDH activity still present in the cytoplasm of the plasmidless derivative. The data demonstrate that E. coli VU3695 contains a chromosomal and a plasmid copy of adhC actively expressed, with the latter being involved in resistance to exogenous formaldehyde.