Role of speA Gene Expression in Streptococcus pyogenes of Infectious Diseases

Streptococcus pyogenes (Group A Streptococcus, GAS) is an important human pathogen that can cause a wide range of clinical conditions, ranging from mild (i.e. pharyngitis) to severe and life-threatening diseases like necrotizing fasciitis and streptococcal toxic shock syndrome. The balance of inducing mild versus invasive disease will likely be determined by several virulence factors such as the pyrogenic exotoxins. The speA gene, which encodes Streptococcal pyrogenic exotoxin A SpeA has been associated with severe invasive disease. The present study is intended to examine the expression of the speA gene in S. pyogenes (group A Streptococcus, GAS) strains recovered from both invasive and mild infections. Twenty clinical isolates of S. pyogenes (10 from patients with invasive infections and 10 from those having mild infections) were used. Gene expression of speA was examined by quantitative real-time PCR (RT-qPCR) with 16S rRNA gene as a reference. Results The level of speA expression were significantly greater in the invasive isolates than those from non-invasive infections and there was a strong correlation between speA expression and the invasiveness of individual invasive isolates. Changes in speA expression, as determined by unpaired statistical analysis with the use of the t-test, were highly significant (p<0.001). In addition, logistic regression analysis showed that speA gene expression was a significantly positive predictor for invasive infection. Our results suggest that speA expression is a potential biomarker that can aid in predicting the pathogenicity nature of S. pyogenes isolates, and may also direct future therapeutic and diagnosis strategies for eradicating these virulence determinants in invasive disease.