Use of phenotypic and molecular serotype identification methods to characterize previously nonserotypeable group B streptococci.
Among 1,762 isolates of Streptococcus agalactiae (group B streptococcus [GBS]), 207 (12%) initially nonserotypeable isolates were tested by improved conventional serotyping methods (Lancefield antigen extraction with 0.1 and 0.2 N HCl, latex agglutination assays, and use of antisera against all known serotypes [Ia, Ib, and II to IX]) and a molecular serotype identification system (multiplex PCR-based reverse line blot [mPCR/RLB] assays targeting serotype-specific sites in the region spanning cpsH to cpsM). Serotypes were assigned to 71 (34%) of the 207 isolates by using antisera and to 204 (98.5%) of them by mPCR/RLB. Sequencing of a portion of the cpsE-cpsF-cpsG region of 141 persistently nonserotypeable isolates and 1 with discrepant conventional and molecular serotyping results was attempted. Major mutations were identified in 34 isolates (24%), including 11 (8%) from which no amplicons were obtained and 23 (16%) with sequence variation compared with published sequences; of the latter, 21 (15%) were associated with amino acid changes. By contrast, mutations were identified in only 12 (2.3%) of 516 serotypeable isolates for which this region has been sequenced previously. In summary, an improved serotyping scheme allowed serotype identification of more than one-third of the previously nonserotypeable GBS isolates. Molecular serotypes were assigned to almost all of the isolates by mPCR/RLB. Significant mutations (with no amplicons or with associated amino acid changes) were found in the cpsE-cpsF-cspG region of a higher proportion of nonserotypeable than of serotypeable isolates (32/141 versus 8/516; P < 0.001), but further investigation is needed to determine the genetic basis for most nonserotypeable GBS isolates.
Kong
Fanrong
F
Centre for Infectious Diseases and Microbiology, Institute of Clinical Pathology and Medical Research, Westmead Hospital, Darcy Road, Westmead, New South Wales 2145, Australia.
Lambertsen
Lotte Munch
LM
Slotved
Hans-Christian
HC
Ko
Danny
D
Wang
Hui
H
Gilbert
Gwendolyn L
GL
D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D015373:Bacterial Typing Techniques / Q000379:methods*; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics; D023061:Gene Order; D005838:Genotype; D006801:Humans; D008969:Molecular Sequence Data; D005810:Multigene Family; D020125:Mutation, Missense; D010641:Phenotype; D016133:Polymerase Chain Reaction / Q000379:methods; D017422:Sequence Analysis, DNA; D012703:Serotyping / Q000379:methods; D013290:Streptococcal Infections / Q000382:microbiology / Q000662:veterinary*; D013292:Streptococcus agalactiae / Q000145:classification* / Q000235:genetics / Q000502:physiology
D001426:Bacterial Proteins; D004269:DNA, Bacterial