Molecular characteristics of Streptococcus agalactiae strains deficient in alpha-like protein encoding genes

Abstract

Streptococcus agalactiae (group B streptococci, GBS) are important human and animal pathogens, which can be subdivided based on different capsular polysaccharides and surface-anchored alpha-like proteins (Alps), as well as other proteins. Nearly all GBS strains possess an Alp (Alp GBS), although Alp-negative GBS (non-Alp GBS) do occur. In this study, 10 (1.1 %) of 932 clinical human GBS tested lacked an Alp encoding gene. All 10 strains were from patients with bloodstream infection, confirming that non-Alp GBS can be highly virulent. All non-Alp GBS expressed one or more of the surface-anchored proteins R3, Z1 and Z2, while less than 10 % of unselected clinical strains express any of these proteins. In contrast to Alp GBS, all non-Alp strains tested were PCR negative for the upstream sequence of the insertion site of the Alp encoding gene of Alp GBS. Genome sequencing showed that all but one of the 10 clinical non-Alp strains and the non-Alp reference strain CNCTC 10/84 lacked a region surrounding the Alp gene commonly present in Alp GBS strains. These strains instead harboured an 849 bp region not present in the Cα prototype strain A909. We have shown that non-Alp GBS differ from Alp GBS in the region surrounding the insertion site of Alp genes of Alp GBS as well as in their content of other surface proteins and that PCR for the upstream flanking region of the Alp gene may be useful for differentiation between Alp and non-Alp GBS.

Progress toward a group B streptococcal vaccine

“…110 Furthermore, over 90% of GBS clinical isolates were found to express or encode at least one of the Alp protein family genes. 113 Seven members of the Alp family, including AlphaC, BetaC, Alp1, Alp2, Alp3 (R28), Alp4, and Rib, have been identified to date. They contain an N-terminal secretion signal sequence (S), N-terminal conserved domain (N), a variable number of tandemly arranged repeats of 70-80 amino acids (R), 8 to 10 repeats, and a C-terminal LPXTG cell-wall anchoring motif (Fig.…”

The Streptococcus agalactiae R3 surface protein is encoded by sar5

“…These strains were previously characterized for R3 expression (and other serotype markers) by fluorescent antibody testing using a monoclonal R3 antibody (18). This R3 antibody has been used and evaluated in several previous studies (6,20,21,(26)(27)(28). We typed the strains for presence/absence of sar5 using a previously established PCR approach (6), with the R3 reference strain CCUG 29784 (also known as Prague 10/84) as a positive control.…”

“…One classification scheme of GBS surface proteins includes Cβ and the Cα-like proteins (Alps) Cα, Alp1-4 and Rib. Nearly all GBS strains carry one of the six alp genes (Alp GBS) although, occasionally, an Alp-encoding gene may be absent (non-Alp GBS) (9). Another, and overlapping, classification system of GBS surface proteins is the Streptococcal R proteins first described in 1952 (10), which are resistant to trypsin digestion (thereby designated “R”).…”

Bacterial and Host Determinants of Group B Streptococcal Vaginal Colonization and Ascending Infection in Pregnancy

“…A vaccine composed of alum-adjuvanted GBS-NN in combination with GBS-NN2, a second fusion peptide derived from N-terminal domains from the other Alps, has been designed (Minervax ApS, Denmark). This vaccine is expected to protect against nearly all GBS clinical isolates since 99% of strains express at least one Alp (Gabrielsen et al, 2017). The results from a phase I randomized double-blind, placebocontrolled study of healthy, non-pregnant women are promising (NCT02459262).…”