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Antimicrobial Agents and Chemotherapy, November 2000, p. 3118-3121, Vol. 44, No. 11
Antimicrobial Agents Research Group, Division
of Infection and Immunity, University of Birmingham, Birmingham,
B15 2TT, United Kingdom,1 and Center for
Veterinary Medicine, Food and Drug Administration, Laurel, Maryland
207082
Received 6 April 2000/Returned for modification 25 May
2000/Accepted 9 August 2000
The mechanism of multiple antibiotic resistance in six isolates of
Salmonella enterica serovar Typhimurium recovered from a
patient treated with ciprofloxacin was studied to investigate the role
of efflux in the resistance phenotype. Compared to the patient's
pretherapy isolate (L3), five of six isolates accumulated less
ciprofloxacin, three of six isolates accumulated less chloramphenicol, and all six accumulated less tetracycline. The accumulation of one or
more antibiotics was increased by carbonyl cyanide
m-chlorophenylhydrazone to concentrations similar to those
accumulated by L3 for all isolates except one, in which accumulation of
all three agents remained approximately half that of L3. All isolates
had the published wild-type sequences of marO and
marR. No increased expression of marA,
tolC, or soxS was observed by Northern
blotting; however, three isolates showed increased expression of
acrB, which was confirmed by quantitative competitive
reverse transcription-PCR. However, there were no mutations within
acrR or the promoter region of acrAB in any of
the isolates.
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Evidence for an Efflux Pump Mediating Multiple
Antibiotic Resistance in Salmonella enterica Serovar
Typhimurium
*
Corresponding author. Mailing address: Antimicrobial
Agents Research Group, Division of Infection and Immunity, University of Birmingham, Birmingham, B15 2TT, United Kingdom. Phone:
0121-414-6969. Fax: 0121-414-6966. E-mail:
l.j.v.piddock{at}bham.ac.uk.
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