Detection and quantification of Streptococcus pneumoniae from Iranian patients with pneumonia and individual carriers by real time PCR

Abstract

The aim of this study was to develop a real time polymerase chain reaction (PCR) for quantitative detection of Streptococcus pneumoniae from clinical respiratory specimens. Initially, 184 respiratory specimens from patients with community acquired pneumonia (CAP) (n = 129) and 55 cases with hospital associated pneumonia (HAP) were bacteriologically investigated. To check the colonization status among the healthy individuals, 32 preschool and 31 adults were screened in parallel. All specimens were cultured on selective culture media to isolate S. pneumoniae, Legionella spp. and Mycoplasma spp. A 166 bp fragment corresponding to cbp A gene of S. pneumoniae was amplified from clinical specimens using Taqman probe real time PCR. Culture showed 14, but real time PCR showed 15 specimens as being positive for S. pneumoniae. The specificity and sensitivity of real time PCR was 99.14% and 100 respectively. Co-infections of S. pneumoniae with Legionella pneumophila, Chlamydophila pneumoniae, Mycoplasma pneumoniae and Staphylococcus aureus were observed in 5 cases (35.72%). S. pneumoniae was counted <10³ cfu/ml from the co-infected cases. Using real time PCR, a cutoff of 10³cfu/ml is introduced to differentiate colonization from infection in respiratory tract. This is the first report on the prevalence CAP with S. pneumoniae in Iran (12.40%).

Key words: Streptococcus pneumoniae, community acquired pneumonia (CAP), real time polymerase chain reaction (PCR), choline binding protein A (cbp A).