Abstract

The Group B Streptococcus (GBS) Surface Immunogenic Protein (Sip) is highly conserved and is present in all serotypes. An analysis of the primary structure determined that the protein contains a secretion signal peptide and a LysM domain that allows it to anchor to the cell wall by binding to peptidoglycan, locating itself on the cell surface along with other proteins characterized as virulence factors in adhesion or invasion. The function of the Sip protein is still unknown; therefore, a mutagenesis strategy aimed at deleting the gene and evaluating its role in classical mechanisms of pathogenesis is important in this line of research. Methods: A strain of GBS mutant sip was obtained using a high-throughput suicide vector (pMBsacB) to generate clean deletions of specific locus. Then, the ability for adhesion and invasion in the cervical epithelium (HeLa) and lung epithelial (A549) cell lines was evaluated. Results: A site-specific deletion directed to the sip gene was generated by homologous recombination with the pBMsacB vector cloned with a recombination cassette, confirming by massive sequencing the success of the deletion. In addition, a decrease in the adhesion capacity was observed in the strain of the GBS mutant sip with respect to the wild-type for both cell lines (i.e., HeLa and A549). No significant differences were observed in the cell invasion capacity in HeLa cells, but GBS mutant sip showed a decrease in its ability to invade A549 cells. Conclusions: The absence of Sip protein in GBS modifies the adhesion and invasion phenotypes in the in vitro model, which suggests a hypothetical function as an adhesin and/or invasin.