JAC Advance Access published online on December 19, 2003
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkh044
© 2003 by The British Society for Antimicrobial Chemotherapy
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Original article
1 Department of Pathology
and Microbiology, University of Bristol, Medical Sciences Building,
University Walk, Bristol BS8 1TD;
* Corresponding author. E-mail: V.I.Enne{at}bristol.ac.uk.
Received 8 August 2003
; revised 24 October 2003
; accepted 3 November 2003
Objectives: The genetic basis of rifampicin
resistance and the associated fitness cost in Enterococcus faecium were
investigated. Methods: Twelve spontaneous rifampicin-resistant E. faecium mutants were selected from four parent strains
recently isolated from porcine faecal material. The DNA sequence
of the complete rpoB gene from the parent strains
and of nucleotides -189 to +1785 from the mutants
was determined from PCR amplicons. The fitness of the mutants was
assessed by determining growth rate, by direct growth competition
and by the ability of some of the mutants to survive in the pig
intestine. Results: The rpoB genes of
the parent strains diverged from each other by 1-10% and
each encoded proteins that were 1208 amino acids in length. All
mutants had a single amino acid substitution in the region implicated
in rifampicin resistance in other organisms. Six mutants carried
the substitution H489Y/Q, two mutants carried the substitution R492H,
one mutant carried the substitution Q480H, two mutants carried the substitutions
S494L and V224I, and one mutant carried the substitutions G485D
and V224I. Per generation fitness costs of the mutants ranged from
a gain of 2.5% to a cost of 10%. Mutants with
the substitution H489Y/Q were the most fit, whereas the double mutants
were the least fit. The mutant with the substitution H489Q was able
to survive in the pig gut for 12 days. There was some correlation
between the rifampicin MIC and fitness cost, with higher MICs being
associated with higher fitness costs. Conclusions: Substitutions in RpoB are associated
with rifampicin resistance in E. faecium. The fitness
cost of resistance is variable and can sometimes be absent.
Keywords: rpoB, biological cost, in
vivo fitness
Rifampicin resistance and its fitness cost in Enterococcus faecium
2 Division of Farm Animal Science, Department of
Clinical Veterinary Science,
University of Bristol, Langford BS40 5DU, UK
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  K. H. Rand, H. J. Houck, and J. A. Silverman Daptomycin-reversible rifampicin resistance in vancomycin-resistant Enterococcus faecium J. Antimicrob. Chemother., May 1, 2007; 59(5): 1017 - 1020. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. I. Enne, A. A. Delsol, G. R. Davis, S. L. Hayward, J. M. Roe, and P. M. Bennett Assessment of the fitness impacts on Escherichia coli of acquisition of antibiotic resistance genes encoded by different types of genetic element J. Antimicrob. Chemother., September 1, 2005; 56(3): 544 - 551. [Abstract] [Full Text] [PDF]
|
|