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Journal of Clinical Microbiology, August 2001, p. 2784-2787, Vol. 39, No. 8
Service de Microbiologie, CHU Côte de
Nacre, 14033 Caen Cedex,1 Laboratoire
Départemental Frank Duncombe, 14053 Caen
Cedex,2 and AFSSA, Laboratoire
d'Études et de Recherche en Pathologie Équine,
Goustranville, 14430 Dozulé,3 France
Received 8 November 2000/Returned for modification 11 March
2001/Accepted 13 May 2001
Treatment with a combination of erythromycin and rifampin has
considerably improved survival rates of foals and immunocompromised patients suffering from severe pneumonia caused by Rhodococcus equi. Frequently, because of monotherapy, emergence of
rifampin-resistant strains has been responsible for treatment failure.
Using consensus oligonucleotides, we have amplified and sequenced the
rifampin resistance (Rifr)-determining regions of 12 rifampin-resistant R. equi strains isolated from three
foals and of mutants selected in vitro from R. equi ATCC
3701, a rifampin-susceptible strain. The deduced amino acid sequences
compared to those of four rifampin-susceptible R. equi
strains showed several types of mutations. In 3 of the 10 strains
isolated from one foal, His526Asn (Escherichia coli numbering) and Asp516Val mutations were associated with low-level resistance (rifampin MIC, 2 to 8 µg/ml), whereas His526Asp conferred high-level resistance (rifampin MIC, 128 µg/ml) in the 7 remaining strains. In strains from the two other foals, His526Asp and
Ser531Leu mutations were found to be associated with high-level and
low-level resistance, respectively. The in vitro mutants, highly
resistant to rifampin, harbored His526Tyr and His526Arg substitutions.
As described in other bacterial genera, His526, Ser531, and Asp516 are
critical residues for rifampin resistance in R. equi,
and the resistance levels are dependent on both the location and the nature of the substitution.
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.8.2784-2787.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Characterization of Mutations in the rpoB Gene
Associated with Rifampin Resistance in Rhodococcus equi
Isolated from Foals
*
Corresponding author. Mailing address: Service de
Microbiologie, CHU Côte de Nacre, Av. Côte de Nacre, 14033, Caen cedex, France. Phone: 33 2 31 06 45 72. Fax: 33 2 31 06 45 73. E-mail: fines-m{at}chu-caen.fr.
Journal of Clinical Microbiology, August 2001, p. 2784-2787, Vol. 39, No. 8
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.8.2784-2787.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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