JAC Advance Access published online on March 13, 2003
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkg168
© 2003 by The British Society for Antimicrobial Chemotherapy
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Original article
1 Área de Bioquímica y Biología
Molecular, Universidad de La Rioja, Madre de Dios 51, 26006, Logroño,
Spain
* Corresponding author. E-mail: carmen.torres{at}daa.unirioja.es.
Received 8 April 2002
; revised 24 July 2002
; accepted 20 January 2003
Mutations in quinolone targets were analysed in 80
unrelated nalidixic acid-resistant (NALR) Escherichia
coli strains whose nalidixic acid and ciprofloxacin MICs ranged
from 32 to >256 mg/L and 0.03-64 mg/L, respectively.
These strains were isolated from food products (23) and faecal samples
from humans (15) and healthy animals (42). Thirteen nalidixic acid-susceptible
(NALS) E. coli strains were also analysed.
Mutations in gyrA and parC genes
were studied by PCR and sequencing. No amino acid changes were detected
in GyrA or ParC proteins of the 13 NALS strains. A single
change in the GyrA protein was detected in all 61 NALR strains
with ciprofloxacin MICs
Keywords: Escherichia coli, quinolone
resistance
Mutations in gyrA and parC genes
in nalidixic acid-resistant Escherichia coli strains
from food products, humans and animals
2 mg/L with
the following substitutions (number of strains): Ser-83
Leu
(54), Ser-83Ala (one), Ser-83Val
(one), Asp-87Asn (two), Asp-87Tyr
(two) and Asp-87Gly (one). A double
change in GyrA was found in 18 of 19 NALR strains with
ciprofloxacin MICs 
4
mg/L. Amino acid substitutions were Ser-83Leu,
with an additional change [Asp-87Asn (15),
Asp-87Tyr (two) or Asp-87His
(one)]. The remaining strain (ciprofloxacin MIC 4 mg/L) showed
a single Ser-83Leu substitution. In
respect of the ParC protein, a single change at Ser-80 or Glu-84
was found in 25 of 42 strains, with ciprofloxacin MICs ranging from
0.5 to 32 mg/L. A double substitution (Ser-80Ile
and Glu-84Gly) was found in one strain
(ciprofloxacin MIC 64 mg/L). No amino acid changes were detected
in the GyrB protein of 18 NALR strains.
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