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Clinical optochin resistant Streptococcus pneumoniae and Streptococcus pseudopneumoniae strains in Tunisia
Sonia Ktari1, Nour El Houda Ben Ayed2, Sonda Maalej2
1Laboratory of Microbiology, Medical School of Sfax, Tunisia. sonia_ktari2002@yahoo.fr.
Introduction:
Streptococcus pneumoniae can be responsible for severe human infections. Optochin resistance has been a potential cause of misidentification of pneumococcus and other members of the mitis group. Hence, rapid and easy optochin resistant (Optr) S. pneumoniae identification is essential.
Methodology:
Atypical pneumococci were characterized using optochin susceptibility, bile solubility based on spectrophotometric reading, serotyping, pulsed field gel electrophoresis (PFGE), 16S rRNA sequencing and PCR-based assays targeting pneumococcal genes lytA, ply, pspA, cpsA, Spn9802 and Spn9828.
Results:
Optical density values for the bile solubility test suggest the identification of four Optr S. pneumoniae and one Streptococcus pseudopneumoniae. All Optr pneumococci harbored cpsA, lytA, ply, Spn9802, Spn9828 and pspA genes. Only ply, spn9802 and Spn9828 genes were detected in S. pseudopneumoniae. The 16S rRNA sequencing differentiates between these two species. Optr S. pneumoniae strains belonged to different genotypes and serotypes (14, 19A, 3 and 9V). Three Optr S. pneumoniae isolates were typed as pspA family 2, while one belonged to pspA family 1. Sequencing of the atpA and atpC gene of the Optr variants revealed three mutations in the ATPase a-subunit (L99I, M23V and V52I) and one mutation in ATPase c-subunit (V48I).
Conclusions:
Our data indicate that bile OD-values provides an accurate, fast and easy method to discriminate between Optr S. pneumoniae and other Streptococcus mitis group. Moreover molecular techniques, confirming the bile test, can be used in order to prevent these atypical pneumococci and alert clinical microbiologists of the presence of these strains in the community.
Insights
Optochin-resistant Streptococcus pneumoniae can be misidentified, but bile solubility tests accurately identify these strains. Molecular methods confirm these atypical pneumococci, aiding clinical microbiologists.
Area of Science:
- Microbiology
- Molecular Biology
Background:
- Streptococcus pneumoniae causes severe infections.
- Optochin resistance can lead to misidentification of pneumococci and other mitis group streptococci.
- Rapid identification of optochin-resistant (Optr) S. pneumoniae is crucial.
Purpose of the Study:
- To develop and validate a rapid and accurate method for identifying optochin-resistant S. pneumoniae.
- To characterize atypical pneumococcal strains using various microbiological and molecular techniques.
Main Methods:
- Optochin susceptibility testing
- Bile solubility testing with spectrophotometric reading
- Serotyping
- Pulsed field gel electrophoresis (PFGE)
- 16S rRNA sequencing
- PCR assays for pneumococcal genes (lytA, ply, pspA, cpsA, Spn9802, Spn9828)
Main Results:
- Bile solubility optical density values accurately differentiated four Optr S. pneumoniae strains and one Streptococcus pseudopneumoniae.
- All Optr pneumococci possessed cpsA, lytA, ply, Spn9802, Spn9828, and pspA genes, while S. pseudopneumoniae only had ply, spn9802, and Spn9828.
- 16S rRNA sequencing distinguished between the two species.
- Optr S. pneumoniae strains exhibited diverse genotypes and serotypes (14, 19A, 3, 9V).
- Specific mutations were identified in the ATPase a-subunit and c-subunit genes of Optr variants.
Conclusions:
- Bile OD values offer an accurate, fast, and simple method to distinguish Optr S. pneumoniae from other Streptococcus mitis group members.
- Molecular techniques confirm bile test results and help prevent misidentification of atypical pneumococci.
- Alerting clinical microbiologists to the presence of these strains is essential for community health.
