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J. Clin. Microbiol. doi:10.1128/JCM.00117-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A proposed new Streptococcus agalactiae serotype, serotype IX

Neisseria and Streptococci Reference laboratory, Department for Bacteriology, Mycology and Parasitology, Statens Serum Institut, Copenhagen, Denmark; Centre for Infectious Diseases and Microbiology-Public Health (CIDM-PH), Institute of Clinical Pathology and Medical Research (ICPMR), Westmead Hospital, Westmead, New South Wales 2145, Australia

^* To whom correspondence should be addressed. Email: hcs{at}ssi.dk.

	Abstract

We identified three isolates of Streptococcus agalactiae (group B streptococcus; GBS), of human origin, which failed to react with antisera against any of the nine known GBS serotypes. Polyclonal rabbit antisera raised against these isolates and standard GBS typing sera were used in capillary precipitation and Ouchterlony tests, to compare the strains with known GBS serotype reference strains. All three previously nontypeable isolates reacted with all three new antisera, producing lines of identity in the Ouchterlony test. Weak cross-reactions with antisera against several GBS serotypes were observed, but were removed by absorption with corresponding antigens. The new antiserum were used to test 227 GBS isolates, that had been nontypeable or difficult to type using standard antisera. Of these, five reacted with the new antiserum. These results suggested that all eight isolates belong to the previously unrecognized GBS serotype. They were tested by Western blot for C and C proteins and by PCR to identify molecular serotypes and surface protein antigen genes. Two segments of the cps gene cluster (3' end of cpsE-cpsF and the 5' end of cpsG, approximately 700 bp; 3' end of cpsH and the 5' end of cpsM approximately 560 bp) were sequenced. All eight isolates express C and seven express C protein and the corresponding genes, bca and bac, respectively, were identified in the relevant isolates. They all share the same, unique partial cps sequence. These results indicate that these eight isolates represent a new S. agalactiae serotype, which we propose should be designated serotype IX.

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