title: Evaluation and improvement of real-time PCR assays targeting lytA, ply, and psaA genes for detection of pneumococcal DNA.
abstract: The accurate diagnosis of pneumococcal disease has frequently been hampered not only by the difficulties in obtaining isolates of the organism from patient specimens but also by the misidentification of pneumococcus-like viridans group streptococci (P-LVS) as Streptococcus pneumoniae. This is especially critical when the specimen comes from the respiratory tract. In this study, three novel real-time PCR assays designed for the detection of specific sequence regions of the lytA, ply, and psaA genes were developed (lytA-CDC, ply-CDC, and psaA, respectively). These assays showed high sensitivity (<10 copies for lytA-CDC and ply-CDC and an approximately twofold less sensitivity for psaA). Two additional real-time PCR assays for lytA and ply described previously for pneumococcal DNA detection were also evaluated. A panel of isolates consisting of 67 S. pneumoniae isolates (44 different serotypes and 3 nonencapsulated S. pneumoniae isolates from conjunctivitis outbreaks) and 104 nonpneumococcal isolates was used. The 67 S. pneumoniae isolates were reactive in all five assays. The new real-time detection assays targeting the lytA and psaA genes were the most specific for the detection of isolates confirmed to be S. pneumoniae, with lytA-CDC showing the greatest specificity. Both ply PCRs were positive for all isolates of S. pseudopneumoniae, along with 13 other isolates of other P-LVS isolates confirmed to be non-S. pneumoniae by DNA-DNA reassociation. Thus, the use of the ply gene for the detection of pneumococci can lead to false-positive reactions in the presence of P-LVS. The five assays were applied to 15 culture-positive cerebrospinal fluid specimens with 100% sensitivity; and serum and ear fluid specimens were also evaluated. Both the lytA-CDC and psaA assays, particularly the lytA-CDC assay, have improved specificities compared with those of currently available assays and should therefore be considered the assays of choice for the detection of pneumococcal DNA, particularly when upper respiratory P-LVS might be present in the clinical specimen.
authors.affiliation: Division of Bacterial Diseases, Centers for Diseases Control and Prevention, Atlanta, GA 30333, USA.
authors.forename: Maria da Gloria S
authors.initials: Mda G
authors.lastname: Carvalho
authors.forename: Maria Lucia
authors.initials: ML
authors.lastname: Tondella
authors.forename: Karen
authors.initials: K
authors.lastname: McCaustland
authors.forename: Luciana
authors.initials: L
authors.lastname: Weidlich
authors.forename: Lesley
authors.initials: L
authors.lastname: McGee
authors.forename: Leonard W
authors.initials: LW
authors.lastname: Mayer
authors.forename: Arnold
authors.initials: A
authors.lastname: Steigerwalt
authors.forename: Melissa
authors.initials: M
authors.lastname: Whaley
authors.forename: Richard R
authors.initials: RR
authors.lastname: Facklam
authors.forename: Barry
authors.initials: B
authors.lastname: Fields
authors.forename: George
authors.initials: G
authors.lastname: Carlone
authors.forename: Edwin W
authors.initials: EW
authors.lastname: Ades
authors.forename: Ron
authors.initials: R
authors.lastname: Dagan
authors.forename: Jacquelyn S
authors.initials: JS
authors.lastname: Sampson
mesh_terms: D002555:Cerebrospinal Fluid / Q000382:microbiology; D002648:Child; D004269:DNA, Bacterial / Q000032:analysis* / Q000235:genetics; D005189:False Positive Reactions; D005798:Genes, Bacterial; D006801:Humans; D009693:Nucleic Acid Hybridization; D010034:Otitis Media with Effusion / Q000382:microbiology; D011008:Pneumococcal Infections / Q000175:diagnosis / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity; D044967:Serum / Q000382:microbiology; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D004269:DNA, Bacterial