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Distribution and expression of bca, the gene encoding the c alpha protein, by Streptococcus agalactiae.

Journal of Medical Microbiology

isolation & purification, Adult, Antibodies, Monoclonal, biosynthesis, immunology, Antigens, Surface, analysis, genetics, Bacterial Proteins, Base Sequence, Blotting, Southern, Cloning, Molecular, Fluorescent Antibody Technique, Gene Expression, Humans, Immunoblotting, Infant, Newborn, Molecular Sequence Data, Polymerase Chain Reaction, methods, Sequence Analysis, DNA, Streptococcal Infections, microbiology, Streptococcus agalactiae, classification

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      A total of 52 clinical isolates of group B streptococci (GBS) was tested for expression of the c protein c(alpha) by a fluorescent antibody test (FAT) and by PCR amplification of a 202-bp stretch within the repeat unit of the bca gene encoding the c(alpha) protein. The strains were categorised as follows: c(alpha) FAT positive and PCR positive with amplification products of multiple sizes (category A, n = 12); FAT negative and with PCR products of multiple sizes (category B, n = 11); FAT negative and with a single PCR product of c. 200 bp (category C, n = 5); negative in both tests (category D, n = 24). A single amplification product of minimum size and additional products of larger sizes corresponded to one and more bca repeats, respectively. Five of the 11 category B strains showed expression of low Mr c(alpha) in whole cell-based Western blotting. The results showed that a proportion of the GBS isolates harboured bca gene elements that either were not expressed or they expressed c(alpha) molecular variants which could not be detected by the whole cell-based FAT. This genotype/phenotype discrepancy should be considered in relation to GBS typing, including the selection of antibody reagents and the technical approach to c(alpha) protein detection.

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