Genetic analysis of Streptococcus pneumoniae serotypes with the use of DNA fingerprinting

Molecular genetic similarities among a Streptococcus pneumoniae library were examined by comparing DNA restriction endonuclease banding patterns (fingerprints) after nuclease digestion and agarose gel electrophoresis. Densitometric scanning graphs of DNA fingerprints on photonegative film were compared for similarity, i.e., the percentage of shared bands. Comparison of serotypes 1, 3, 12, 14, and 25 revealed 54% +/- 9% similarity. Fingerprints within serogroups IX and XVIII did not differ from non-cross-reactive types. Intraserotypic comparison of strains of type 25 (n = 5) revealed 89% +/- 4% similarity. Five strains of type 3 were 75% +/- 19% similar; however, two of these strains had 96% similarity and three strains had 98% +/- 2% similarity, perhaps suggesting subtypes with serotype 3. Substantial DNA fingerprint differences were found among serotypes and significantly greater similarity among strains of a given type. Thus, DNA analyses used on other gram-positive bacteria are applicable to pneumococci.