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Antimicrobial Agents and Chemotherapy, September 2002, p. 2747-2751, Vol. 46, No. 9
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.9.2747-2751.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Evaluation of Antibiotic Susceptibilities of Three Rickettsial Species Including Rickettsia felis by a Quantitative PCR DNA Assay

Jean-Marc Rolain, Laetitia Stuhl, Max Maurin, and Didier Raoult*

Unité des Rickettsies CNRS UPRES-A 6020, Faculté de Médecine, Université de la Méditerranée, 13385 Marseille Cedex 05, France

Received 4 January 2002/ Returned for modification 29 March 2002/ Accepted 15 May 2002

Rickettsiae grow only intracellularly, and the antibiotic susceptibilities of these bacteria have been assessed by either plaque, dye uptake, or immunofluorescence assays, which are time-consuming. We used a quantitative PCR (with the LightCycler instrument) to assess the levels of inhibition of Rickettisa felis, R. conorii, and R. typhi DNA synthesis in the presence of various antibiotics. We established the kinetics of rickettsial DNA during growth and showed that R. conorii grows more quickly than R. typhi in cell culture, with maximum replication occurring after 5 and 7 days, respectively. The MICs of the antibiotics tested for R. conorii and R. typhi by the quantitative PCR assay were similar to those previously obtained by plaque and dye uptake assays. We found that R. felis is susceptible to doxycycline, rifampin, thiamphenicol, and fluoroquinolones but not to gentamicin, erythromycin, amoxicillin, or trimethoprim-sulfamethoxazole. The resistance of this new species to erythromycin is consistent with its current taxonomic position within the spotted fever group. We believe that quantitative PCR could be used in the future to simplify and shorten antibiotic susceptibility assays of other rickettsiae and other strict intracellular pathogens.

* Corresponding author. Mailing address: Unité des Rickettsies, Faculté de Médecine, 27, Blvd. Jean Moulin, 13385 Marseille Cedex 5, France. Phone: 33.04.91.32.43.75. Fax: 33.04.91.38.77.72. E-mail: Didier.Raoult{at}medecine.univ-mrs.fr.

Antimicrobial Agents and Chemotherapy, September 2002, p. 2747-2751, Vol. 46, No. 9
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.9.2747-2751.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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