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Laboratory diagnosis of Mycoplasma pneumoniae infection: 2. Comparison of methods for the direct detection of specific antigen or nucleic acid sequences in respiratory exudates

Published online by Cambridge University Press:  15 May 2009

R. Harris
Affiliation:
School of Pharmacy and Medical Laboratory Science, S.A. Institute of Technology, Adelaide.
B. P. Marmion*
Affiliation:
Department of Pathology, University of Adelaide. Division of Medical Virology, Institute of Medical and Veterinary Science, Adelaide.
G. Varkanis
Affiliation:
Division of Medical Virology, Institute of Medical and Veterinary Science, Adelaide.
T. Kok
Affiliation:
Division of Medical Virology, Institute of Medical and Veterinary Science, Adelaide.
B. Lunn
Affiliation:
School of Pharmacy and Medical Laboratory Science, S.A. Institute of Technology, Adelaide.
J. Martin
Affiliation:
Department of Pulmonary Medicine, Adelaide Children's Hospital
*
Please address correspondence and reprint requests to Professor B. P. Marmion, Medical Virology, Institute of Medical and Veterinary Science, box 14, Rundle Mall Post Office, Adelaide, South Australia, 5000.
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Summary

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The efficiency of the direct detection of Mycoplasma pneumoniae in respiratory exudates by an antigen capture, indirect enzyme immunoassay (Ag-EIA), has been compared with its detection with a cDNA probe (‘Gen-Probe assay’) directed against the specific ribosomal RNA sequences of the organism (‘Mycoplasma pneumoniae Rapid Diagnostic System’, Gen-Probe, San Diego, California).

Both assays showed excellent specificity against a range of mycoplasma species suspended in negative nasopharyngeal aspirates; only M. pneumoniae and M. genitalium reacted. In experiments with graded doses of viable M. pneumoniae cells suspended in negative nasopharyngeal aspirate, the Gen-Probe assay was more sensitive than Ag-EIA; detection limits were respectively 2 × 103 c.f.u./ml (3·2 × 105 genomes) and 2·5 × 104 c.f.u./ml (4 × 106 genomes); detection levels 10–100 times less sensitive than culture.

The two assays were also tested on nasopharyngeal aspirates or sputum specimens from 90 patients with respiratory infection; 67 of these were culture-or seronegative for M. pneumoniae and 23 were culture-or seropositive. Ag-EIA detected 21 (91%) of the latter but the Gen-Probe assay detected only 5 (22%). Both assays were negative with the 67 culture-/sero-negatives; there were no Gen-Probe assay positive/Ag-EIA negatives.

Overall, it is concluded that although Ag-EIA and the Gen-Probe assay are effective substitutes for culture as a diagnostic procedure, there is a significant problem with samples which are culture-negative and from patients who have good serological evidence of current infection. Possible reasons for the disparity between the two assays are advanced.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1988

References

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