Accurate identification of Streptococcus pseudopneumoniae and other mitis group Streptococci identified as atypical Streptococcus pneumoniae in Tunisian pediatric population

Accurate identification of Mitis group streptococci especially Streptococcus pneumoniae and Strepto-coccus pseudopneumoniae seems difficult due to the lack of specific and sensitive tests. We performed an approach for the identification of atypical pneumococci in pediatric Tunisian population. In this study, 49 streptococcal isolates that were considered as atypical S. pneumoniae were analyzed by: optochin susceptibility in ambient and 5% CO2 atmosphere, oxgall disk sensitivity, PCR targeting several genes and antimicrobial susceptibility. The combined results of biochemical and molecular methods showed the presence of 23 S. pneu-moniae, 7 S. pseudopneumoniae, and 19 other mitis group. Among S. pseudopneumoniae, all isolates were collected from respiratory tract samples and showed a high level of resistance to beta-lactams with a MIC90 of 32 mg L-1. Two isolates of S. pseudopneumoniae showed the typical phenotype of optochin resistance described in the literature. All isolates could be identified only by molecular tests. Among Streptococcus pneumonaie, all strains harbored the lytA gene and the Spn9802 fragment. But only 14 strains were encapsulated. This study describes several assays for the identification of atypical pneumococci in order to gain insights on the nature of isolate and raise alert about the presence of these strains in the pediatric Tunisian community.