Impact of Laboratory Methods and Gene Targets on Detection of Streptococcus pneumoniae in Isolates and Clinical Specimens

Timely identification of Streptococcus pneumoniae infections can lead to a decrease in mortality rates. Differentiation of S. pneumoniae from other similar species using traditional culture-based and molecular methods is problematic. In this study, we assessed the efficacy of identifying the blpA and lytA for the detection of S. pneumoniae from isolates and various clinical samples using molecular methods.

A total of 440 clinical samples were collected from patients with suspected invasive pneumococcal infections during February 2016 to October 2018. Biochemical tests were used to confirm the dubious colonies on 5% sheep blood agar. Fifty-seven confirmed isolates, 57 culture-positive samples, and 57 culture-negative samples were analyzed for the presence of blpA and lytA using both conventional and real-time PCR.

All the isolates and culture-positive samples were positive for blpA and lytA by both PCR methods. Of the 57 culture-negative samples, conventional and real-time PCR amplified blpA from six and two samples, and lytA from seven and two samples, respectively.

The specificity of real-time PCR assay was significantly higher than that of conventional PCR for the identification of S. pneumoniae. In addition, it is suggested that respiratory secretions are not suitable specimen for direct diagnosis of pneumococcal infections.