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Journal of Clinical Microbiology, October 2003, p. 4573-4577, Vol. 41, No. 10
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.10.4573-4577.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Laboratoire de Bactériologie,1 Service d'Hépato-Gastroentérologie,2 Département de Pathologie, Centre Hospitalo-Universitaire Henri-Mondor, Assistance Publique-Hôpitaux de Paris, Université Paris XII, Créteil,4 Laboratoire de Biologie Moléculaire, Hôpital Américain de Paris, Neuilly,3 Laboratoire de Bactériologie, Centre Hospitalo-Universitaire Saint-Antoine, Assistance Publique-Hôpitaux de Paris, Université Paris VI, Paris, France5
Received 4 April 2003/ Returned for modification 11 June 2003/ Accepted 4 July 2003
Rapid identification of patients infected with clarithromycin-resistant Helicobacter pylori without the need for culture can help to avoid useless prescriptions of clarithromycin. We developed and tested a routine real-time quantitative PCR assay dedicated to that purpose. One hundred ninety-six consecutive gastric biopsy specimens were examined by culture, histology performed by a trained physician, and rapid PCR with the LightCycler apparatus. Infection was defined as (i) positivity of culture, (ii) positivity of histology, or (iii) positivity of PCR if confirmed by positivity of a concomitant indirect test (serology or urea breath test). Susceptibility to clarithromycin was tested by E-test and PCR. The prevalence of infection was 33.7% (66 of 196 samples). The sensitivities of culture, histology, and PCR were 90.9% (60 of 66 samples), 87.9% (58 of 66 samples), and 97.0% (64 of 66 samples), respectively. The specificity of PCR was 94.6% (123 of 130 samples). The linearity of the PCR results was achieved over a 6-log range of input DNA, and we were able to accurately quantify as few as 300 bacteria and to qualitatively detect as few as 30 bacteria per DNA sample. For clarithromycin susceptibility testing, there was 98.2% (55 of 56 samples) concordance between E-test and PCR. Forty-eight strains were clarithromycin susceptible, and 9 strains were clarithromycin resistant. The single discrepancy concerned a culture which was a mixture of mutant and wild type, with a susceptible-to-resistant ratio of 11.5: the resistant population was detected by E-test but not by PCR. Our PCR assay is accurate for fast detection of H. pylori as well as of clarithromycin resistance and is also able to objectively determine bacterial density.
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