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Journal of Clinical Microbiology, April 2006, p. 1250-1256, Vol. 44, No. 4
0095-1137/06/$08.00+0     doi:10.1128/JCM.44.4.1250-1256.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Characteristic Signatures of the lytA Gene Provide a Basis for Rapid and Reliable Diagnosis of Streptococcus pneumoniae Infections

Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain

Received 27 October 2005/ Returned for modification 5 January 2006/ Accepted 23 January 2006

The nucleotide sequences of the lytA gene from 29 pneumococcal isolates of various serotypes and 22 additional streptococci of the mitis group (including two Streptococcus pseudopneumoniae strains) have been compared and found to correspond to 19 typical (927-bp-long) and 20 atypical (921-bp-long) alleles. All the Streptococcus pneumoniae strains harbored typical lytA alleles, whereas nonpneumococcal isolates belonging to the mitis group always carried atypical alleles. A sequence alignment showed that the main difference between typical and atypical lytA alleles resided in 102 nucleotide positions (including the 6 bp absent from atypical alleles). These nucleotides were perfectly conserved in all the typical alleles studied, and the corresponding nucleotides of the atypical alleles were also perfectly conserved. The presence in these signatures of distinctive restriction sites (namely, SnaBI, XmnI, and BsaAI) allowed the development of a simple, reliable, and fast method that combines PCR amplification of the lytA gene, digestion with BsaAI, and separation of the products by agarose gel electrophoresis. This assay allows the rapid and consistent identification of true S. pneumoniae strains and represents an improved diagnostic tool for the study of pneumococcal carriage.

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