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Antimicrobial Agents and Chemotherapy, January 1998, p. 88-93, Vol. 42, No. 1
Laboratory for Molecular Biology, Department
of Biological Sciences, University of Illinois at Chicago, Chicago,
Illinois 60607
Received 22 May 1997/Returned for modification 7 August
1997/Accepted 28 October 1997
A sulfathiazole-resistant dihydropteroate synthase (DHPS) present
in two different laboratory strains of Escherichia coli repeatedly selected for sulfathiazole resistance was mapped to folP by P1 transduction. The folP mutation in
each of the strains was shown to be identical by nucleotide sequence
analysis. A single C
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Characterization of Mutations Contributing to
Sulfathiazole Resistance in Escherichia coli


T transition resulted in a Pro
Ser
substitution at amino acid position 64. Replacement of the mutant
folP alleles with wild-type folP significantly
reduced the level of resistance to sulfathiazole but did not abolish
it, indicating the presence of an additional mutation(s) that
contributes to sulfathiazole resistance in the two strains. Transfer of
the mutant folP allele to a wild-type background resulted
in a strain with only a low level of resistance to sulfathiazole,
suggesting that the presence of the resistant DHPS was not in itself
sufficient to account for the overall sulfathiazole resistance in these
strains of E. coli. Additional characterization of an
amplified secondary resistance determinant, sur, present in
one of the strains, identified it as the previously identified bicyclomycin resistance determinant bcr, a member of a
family of membrane-bound multidrug resistance antiporters. An
additional mutation contributing to sulfathiazole resistance,
sux, has also been identified and has been shown to
affect the histidine response to adenine sensitivity displayed by these
purU strains.
*
Corresponding author. Mailing address: Laboratory for
Molecular Biology, Department of Biological Sciences, Molecular Biology Research Building m/c 567, University of Illinois at Chicago, 900 S. Ashland Ave., Chicago, IL 60607. Phone: (312) 996-5064. Fax: (312)
413-2691. E-mail: brian.p.nichols{at}uic.edu.
Present address: Department of Microbiology, Strich School of
Medicine, Loyola University of Chicago, Maywood, IL 60153.
Present address: Gillette Company, Boston, MA 02127.
§
Present address: Department of Cellular, Molecular and Structural
Biology, Northwestern University Medical School, Chicago, IL 60611.
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