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J Med Microbiol 55 (2006), 775-783; DOI: 10.1099/jmm.0.46253-0
© 2006 Society for General Microbiology
ISSN 1473-5644

Identification of novel cps locus polymorphisms in nontypable group B Streptococcus

Srinivas V. Ramaswamy1, Patricia Ferrieri2, Lawrence C. Madoff1, Aurea E. Flores2, Nikhil Kumar3, Hervé Tettelin3 and Lawrence C. Paoletti1

1 Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA

2 Departments of Laboratory Medicine and Pathology and Pediatrics, University of Minnesota Medical School, Minneapolis, MN 55455, USA

3 The Institute for Genomic Research, 9712 Medical Center Drive, Rockville, MD 20850, USA

Correspondence
Lawrence C. Paoletti
lpaoletti{at}channing.harvard.edu

Received 19 July 2005
Accepted 7 February 2006

Group B Streptococcus (GBS) is an important pathogen responsible for a variety of diseases in newborns and the elderly. A clinical GBS isolate is considered nontypable (NT) when serological methods fail to identify it as one of nine known GBS serotypes. Eight clinical isolates (designated A1–A4, B1–B4) showed PFGE profiles similar to that of a GBS serotype V strain expressing R1, R4 surface proteins. These unique isolates were further characterized by immunologic and genetic methods. Rabbit sera to isolates A1 and A2 reacted weakly with concentrated HCl extracts of A1–A4 isolates, but not with those of B1–B4 isolates. In addition, a type V capsular polysaccharide (CPS) inhibition ELISA revealed that cell wall extracts from isolates A1–A4, but not from B1–B4, expressed low but measurable amounts of type V CPS. Molecular serotyping with PCR analysis showed that all eight isolates contained a type V-specific CPS gene (cpsO) and harboured the gene encoding the surface protein Alp3. Multilocus sequence typing identified isolate A1 as belonging to a new sequence type (ST) designated ST-173, whereas the other seven isolates keyed to ST-1. Sequencing of the 18 genes (17 736 bp) in the cps locus showed that each NT isolate harboured one to three unique polymorphisms, and also identified an IS1381 element in cpsE of the B4 isolate. Collectively, genetic and immunologic analyses revealed that these NT isolates expressing R1, R4 proteins have a genetic profile consistent with that of type V, an emergent, antigenically diverse and increasingly prevalent GBS serotype.

Abbreviations: CPS, capsular polysaccharide; GBS, Group B Streptococcus; MLST, multilocus sequence typing; NT, nontypable; ST, sequence type.

The GenBank/EMBL/DDBJ accession numbers for the sequences reported in this paper are DQ359707–DQ359714.




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