Application ofan Indirect Immunofluorescence TestforDetection of Mycoplasma pneumoniae inRespiratory Exudates

testtodetect thespecific antigen inrespiratory exudates. Theantibody didnotcross-react withnormalhumanserum or withrespiratory exudates from10 healthy persons.Cross-reactivity oftheantibody withspecies ofmycoplasmas otherthanM.genitalium was fully diminished whenabsorbed withhorse serum andyeastextract, componentsoftheculture medium. Thoughtheabsorbed antibody cross-reacted withM.genitalium, thetiter was significantly lowerthanwhen tested against M.pneumoniae. Twotypesofantigen-specific fluorescence were observed inclinical specimens: oneislarge orsmall fluorescent granular aggregates foundinmucus,andtheother isfine fluorescent particles diffused on theentire surface ofsmallepithelial cells. Throat smears from49patients withserologically confirmed M.pneumoniae infections were examined byour indirect immunofluorescence method. Positive results were obtained in42cases,many ofwhich were positive before a rise inserum antibody titer couldbe demonstrated, indicating thatthemethodisuseful for apreliminary diagnosis atan early stageoftheinfection. Mycoplasma pneumoniae causes respiratory tract infection. Thisinfection istraditionally diagnosed byisolating the organism orbydemonstrating arise inserumantibody titer. Isolation oftheorganism takes several weeksbecause ofits slowgrowthinculture. Theserologic testsusedmost commonlyarethecoldhemagglutinin test, thepassive hemagglutination test, andthecomplement fixation (CF)test (23-26). Thecoldhemagglutinin testisnotspecific, anda positive assayisobserved inonlyone-half ofthepatients withM.pneumoniae infection. Theantibodies detected by thepassive hemagglutination andCF tests develop several weeksafter onsetofinfection, andpaired serumsamples (i.e., serumsamples takenduring theacutephaseofthe infection andatleast 1to3weekslater) mustoften betested foradefinitive diagnosis. Theselaboratory tests areusually usedtoevaluate theinfection retrospectively because ofthe intrinsic delay inobtaining theresults. Forpractical use, therefore, anewmethodwhichallows thediagnosis much earlier during thecourse oftheinfection mustbedeveloped. Recently, moresensitive and/or rapid laboratory tests for diagnosis ofM.pneumoniae infections havebeenexamined byusing twoapproaches. Oneistouseamethodcapable of detecting specific anti-M. pneumoniae immunoglobulin M (IgM)orIgGbyenzyme-linked immunosorbent assayor immunoblotting (2,4,8,14,17,19,29). Theother istousea methodtodirectly detect M.pneumoniae present inrespiratory exudates. TheDNA probemethod(7,9-11, 15,16, 22,27), theantigen capture enzymeimmunoassay (Ag-EIA) (10, 18,30), themonoclonal antibody immunoblot assay (21), andthepolymerase chain reaction (3)haveallbeenapplied tothelatter approach, anda DNA probeiscurrently commercially available. Another useful methodtodetect the antigen istheindirect immunofluorescence methodofHers etal.(13). Although thismethodseemstoberapid and capable ofdetecting adistribution oftheantigen, problems ofspecificity exist. Inanattempt toimprove thespecificity ofthis method, we examined preparations ofantibody and