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Journal of Clinical Microbiology, September 2000, p. 3420-3428, Vol. 38, No. 9
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Genotyping of the Capsule Gene Cluster
(cps) in Nontypeable Group B Streptococci Reveals Two Major
cps Allelic Variants of Serotypes III and VII
Mats
Sellin,1,*
Carin
Olofsson,1
Stellan
Håkansson,2 and
Mari
Norgren1
Department of Clinical
Bacteriology1 and Department of
Pediatrics,2 Umeå University, S-901 85 Umeå,
Sweden
Received 21 December 1999/Returned for modification 29 May
2000/Accepted 12 July 2000
Forty group B Streptococcus (GBS) isolates obtained
from Europe and the United States previously reported to be nontypeable (NT) by capsule serotype determination were subjected to buoyant density gradient centrifugation. From nearly half of the isolates capsule-expressing variants could be selected. For characterization of
the remaining NT-GBS isolates, the capsule operon (cps) was amplified by the long-fragment PCR technique and compared by
restriction fragment length polymorphism (RFLP) analysis. The patterns
from serotype reference isolates (n = 32) were first
determined and used as a comparison matrix for the NT-GBS isolates.
Using two restriction enzymes, SduI and AvaII,
cluster analysis revealed a high degree of similarity within serotypes
but less than 88% similarity between serotypes. However, serotypes III
and VII were each split in two distant RFLP clusters, which were
designated III1 and III2 and VII1
and VII2, respectively. Among the isolates that remained NT
after repeated Percoll gradient selections, two insertional mutants
were revealed. Both were found in blood isolates and harbored insertion
sequence (IS) elements within cpsD: one harbored
IS1548, and the other harbored IS861. All other
NT-GBS isolates could, by cluster analysis, be referred to different serotypes by comparison to the RFLP reference matrix. In pulsed-field gel electrophoresis of SmaI-restricted chromosomal DNA,
patterns from allelic type 1 and 2 isolates were essentially
distributed in separate clusters in serotypes III and VII. A
covariation with insertion sequence IS1548 in the
hylB gene was suggested for serotype III, since allelic
type III1 harboring IS1548 in hylB,
clustered separately. The variation in serotype VII was not dependent
on the presence of IS1548, which was not detected at any
position in the type VII chromosome.
*
Corresponding author. Mailing address: Department of
Clinical Bacteriology, Umeå University, S-901 85 Umeå, Sweden. Phone: 46 90 7851123. Fax: 46 90 7852225. E-mail:
mats.sellin{at}climi.umu.se.
Journal of Clinical Microbiology, September 2000, p. 3420-3428, Vol. 38, No. 9
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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