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Abstract
A total of 52 clinical isolates of group B streptococci (GBS) was tested for expression of the c protein cα 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 cα protein. The strains were categorised as follows: cα 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 = ); 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 cα 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 cα 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 cα protein detection.
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