Abstract
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. 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. 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). 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.
Highlights
Streptococcus pneumoniae can be responsible for severe human infections
Slotved et al presented cut-off OD-values that can be used for differentiating S. pneumoniae and S. pseudopneumoniae from other mitis group streptococci [16]
The occurrence of optochin resistant (Optr) S. pneumoniae variants has hampered the phenotypic identification of pneumococci
Summary
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. Optochin resistance has been a potential cause of misidentification of pneumococcus due to the complexity to distinguish Optr S. pneumoniae from S. pseudopneumoniae or other closely related streptococci [9,10,11,12,13,14,15,16,17,18]. The low incidence and potential pathogenic role of S. pseudopneumoniae has been demonstrated in a murine model as well as in humans [11,13]. This bacterium may be associated with chronic obstructive pulmonary disease [12,18]. S. pseudopneumoniae is optochin resistant in the presence of 5% CO2 and optochin susceptible in ambient atmosphere, bile insoluble and lacks the pneumococcal capsule [9]
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