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Antimicrobial Agents and Chemotherapy, 08 1995, 1700-1703, Vol 39, No. 8
GJ Alangaden, EK Manavathu, SB Vakulenko, NM Zvonok and SA Lerner
To examine the mechanism of resistance to fluoroquinolones in Mycobacterium
tuberculosis, we selected spontaneous fluoroquinolone- resistant mutants
from a susceptible strain, H37Rv, and studied the susceptibilities of these
mutants and two fluoroquinolone-resistant clinical isolates (A-382, A-564)
to various fluoroquinolones and to isoniazid and rifampin. Furthermore,
since mutations within the quinolone resistance-determining region of the
structural gene encoding the A subunit of DNA gyrase are the most common
mechanism of acquired resistance, we amplified this region by PCR and
compared the nucleotide sequences of the fluoroquinolone-resistant strains
with that of the susceptible strain. Fluoroquinolone-resistant mutants of
H37Rv appeared at frequencies of 2 x 10(-6) to 1 x 10(-8). For three
mutants selected on ciprofloxacin, ofloxacin, and sparfloxacin,
respectively, and the two clinical isolates, MICs of ciprofloxacin and
ofloxacin were as high as 16 micrograms/ml, and those of sparfloxacin were
4 to 8 micrograms/ml. They displayed cross-resistance to all
fluoroquinolones tested but not to isoniazid or rifampin. Sparfloxacin and
FQ-A (PD 127391-0002) were the most potent fluoroquinolones. All of the
fluoroquinolone-resistant strains (MICs, > or = 4 micrograms/ml) had
mutations in the quinolone resistance-determining region which led to
substitution of the Asp residue at position 87 (Asp-87) by Asn or Ala or
the substitution of Ala-83 by Val in the A subunit of DNA gyrase. Similar
mutations have been noted in other bacterial species and recently in
mycobacteria.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995 by the American Society for Microbiology. All rights reserved.
Characterization of fluoroquinolone-resistant mutant strains of Mycobacterium tuberculosis selected in the laboratory and isolated from patients
Division of Infectious Diseases, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
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