title: Laboratory diagnosis of Mycoplasma pneumoniae infection. 2. Comparison of methods for the direct detection of specific antigen or nucleic acid sequences in respiratory exudates.
abstract: 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 X 10(3) c.f.u./ml (3.2 X 10(5) genomes) and 2.5 X 10(4) c.f.u./ml (4 X 10(6) 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.
authors.affiliation: School of Pharmacy, S.A. Institute of Technology, Adelaide.
authors.forename: R
authors.initials: R
authors.lastname: Harris
authors.forename: B P
authors.initials: BP
authors.lastname: Marmion
authors.forename: G
authors.initials: G
authors.lastname: Varkanis
authors.forename: T
authors.initials: T
authors.lastname: Kok
authors.forename: B
authors.initials: B
authors.lastname: Lunn
authors.forename: J
authors.initials: J
authors.lastname: Martin
mesh_terms: D000942:Antigens, Bacterial / Q000032:analysis; D015342:DNA Probes; D006801:Humans; D007124:Immunoenzyme Techniques; D009177:Mycoplasma pneumoniae / Q000235:genetics* / Q000276:immunology; D009693:Nucleic Acid Hybridization; D011019:Pneumonia, Mycoplasma / Q000175:diagnosis*; D012335:RNA, Ribosomal / Q000032:analysis; D012698:Serologic Tests / Q000379:methods; D013045:Species Specificity
chemical_list: D000942:Antigens, Bacterial; D015342:DNA Probes; D012335:RNA, Ribosomal