Evaluation of lytB Gene for Detection of Streptococcus pneumoniae in Isolates and Clinical Specimens by Real-Time PCR

Background: Streptococcus pneumoniae is a causative agent of morbidity and mortality worldwide. Diagnosis of pneumococcal infection includes conventional culture-based and molecular methods. Differentiation of S. pneumoniae from other mitis group streptococci is not reliable. Objectives: We aimed to evaluate the efficacy of lytB gene along with lytA gene for detection of S. pneumoniae in isolates and clinical samples using conventional and real-time PCR methods. Methods: In this cross-sectional study, a total of 560 clinical specimens were collected from patients during February-September 2015. The samples were cultured on 5% sheep blood agar and suspected colonies were identified by biochemical assays. The antibiotic susceptibility test was performed by disk diffusion and serial microdilution methods. 46 culture-negative and 46 culturepositive samples were examined to evaluate the presence of lytA and lytB genes using conventional and real-time PCR methods. Results: A total of 46 (8.2%) isolates of S. pneumoniae were identified in suspected specimens. 52% (24/ 46) of isolates exhibited multiple drug resistance (MDR). All 46 isolates contained both lytA and lytB genes. Real-time PCR assay detected both genes with low CT values in culture-positive samples. Among culture negative specimens, one sample was positive for both the genes. Conclusions: The lytB is similar to lytA in sensitivity for diagnosis of S. pneumoniae in isolates and clinical samples based on both the molecular methods. The results confirmed the applicability of real time PCR based on lytB genes for detection of S. pneumoniae.