Distribution and expression of bca, the gene encoding the c alpha protein, by Streptococcus agalactiae.
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.
Maeland
J A
JA
Brakstad
O G
OG
Department of Microbiology, School of Medicine, Norwegian University of Science and Technology, N-7006, Trondheim and *SINTEF Applied Chemistry, N-7465, Trondheim, Norway.
Bevanger
L
L
Krokstad
S
S
D000328:Adult; D000911:Antibodies, Monoclonal / Q000096:biosynthesis / Q000276:immunology; D000954:Antigens, Surface / Q000032:analysis / Q000235:genetics*; D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics*; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D006801:Humans; D015151:Immunoblotting; D007231:Infant, Newborn; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D017422:Sequence Analysis, DNA; D013290:Streptococcal Infections / Q000382:microbiology*; D013292:Streptococcus agalactiae / Q000145:classification* / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification
D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D001426:Bacterial Proteins; C077961:alpha C protein, group B streptococci