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Antimicrobial Agents and Chemotherapy, December 2004, p. 4822-4828, Vol. 48, No. 12
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.12.4822-4828.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Evaluation of Antibiotic Susceptibilities of Ehrlichia canis, Ehrlichia chaffeensis, and Anaplasma phagocytophilum by Real-Time PCR

S. Branger, J. M. Rolain, and D. Raoult*

Unité des Rickettsies, CNRS UMR 6020A, Faculté de Médecine, Marseille, France

Received 18 December 2003/ Returned for modification 14 March 2004/ Accepted 4 September 2004

We determined MICs of antibiotics against Anaplasma phagocytophilum, Ehrlichia chaffeensis, and Ehrlichia canis by real-time quantitative PCR. The doubling times of the organisms were established: 19 h for E. chaffeensis, 26 h for A. phagocytophilum, and 28 h for E. canis. In comparison to the reference method for determining sensitivities, which uses Diff-Quick staining, our PCR assay was very sensitive and specific. We confirmed that doxycycline and rifampin are highly active against these bacteria and found variable susceptibilities to fluoroquinolones; A. phagocytophilum was susceptible, but E. canis and E. chaffeensis were only partly susceptible. ß-Lactam compounds, cotrimoxazole, macrolide compounds, and telithromycin showed no activity against any of the three organisms. Thiamphenicol was found to be more active than chloramphenicol. For the first time, we showed that these three species have numerous point mutations in their 23S RNA genes, with those at positions 754, 2057, 2058, 2059, and 2611 (Escherichia coli numbering) known to confer resistance to macrolide compounds in other bacteria. The role of each of these mutations in resistance to these drugs should be investigated in the future. Our study confirms previous reports that quantitative PCR is a reliable method for determining antibiotic susceptibility; therefore, it might be useful for screening new drugs.

* Corresponding author. Mailing address: Unité des Rickettsies, CNRS UMR 6020A, Faculté de Médecine, 27 boulevard Jean Moulin, 13385 Marseille cedex 5, France. Phone: 33 04 91 38 55 17. Fax: 33 04 91 83 03 90. E-mail: Didier.Raoult{at}medecine.univ-mrs.fr.

Antimicrobial Agents and Chemotherapy, December 2004, p. 4822-4828, Vol. 48, No. 12
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.12.4822-4828.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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