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Journal of Clinical Microbiology, August 2003, p. 3521-3525, Vol. 41, No. 8
0095-1137/03/$08.00+0     DOI: 10.1128/JCM.41.8.3521-3525.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Comparison of Five Genotypic Techniques for Identification of Optochin-Resistant Pneumococcus-Like Isolates

Rita Verhelst,1* Tarja Kaijalainen,2 Thierry De Baere,1 Gerda Verschraegen,1 Geert Claeys,1 Leen Van Simaey,1 Catharine De Ganck,1 and Mario Vaneechoutte1

Department of Chemistry, Microbiology and Immunology, Ghent University Hospital, Gent, Belgium,1 National Reference Laboratory for Pneumococcus, National Public Health Institute, Oulu, Finland2

Received 31 December 2002/ Returned for modification 3 March 2003/ Accepted 8 May 2003

Three PCR techniques (amplification of the psaA, ply, and lytA genes) and a commercial kit (AccuProbe [GenProbe, San Diego, Calif.], based on hybridization with the 16S rRNA gene), all four of which claimed to be specific for Streptococcus pneumoniae, were used to identify 49 alpha-hemolytic streptococcal isolates suspected of being pneumococci. The definite phenotypic identification of these organisms as S. pneumoniae was difficult when optochin susceptibility and the presence of a capsule were taken as markers. Furthermore, RsaI digestion of the amplified 16S rRNA gene was applied. All 49 strains were optochin resistant. Eleven of these were encapsulated and were identified as pneumococci by all tests. Twenty of the 38 unencapsulated strains were unambiguously identified as nonpneumococci by all tests. The identities of another 18 unencapsulated strains remained inconclusive due to highly variable reactions for all phenotypic and genotypic techniques applied. The AccuProbe test was positive for seven strains for which the results of the other tests were inconclusive. RsaI restriction of the amplified 16S rRNA gene confirmed the AccuProbe result for all strains, while the result of the psaA-specific PCR was in concordance with encapsulation for all strains. The results presented here indicate that identification problems continue to exist for some strains, despite the application of genotypic and phenotypic tests in combination. We found the psaA-specific PCR to be the genotypic technique best suited for the identification of genuine pneumococci and optochin-resistant pneumococci.

* Corresponding author. Mailing address: Laboratory Bacteriology & Virology, Blok A, Ghent University Hospital, De Pintelaan 185, B9000 Gent, Belgium. Phone: 32 9 240 36 43. Fax: 32 9 240 36 59. E-mail: Rita.Verhelst{at}ugent.

Journal of Clinical Microbiology, August 2003, p. 3521-3525, Vol. 41, No. 8
0095-1137/03/$08.00+0     DOI: 10.1128/JCM.41.8.3521-3525.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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