Abstract
The porcine pathogen Streptococcus suis colonizes the upper respiratory tracts of pigs, potentially causing septicaemia, meningitis and death, thus placing a severe burden on the agricultural industry worldwide. It is also a zoonotic pathogen that is known to cause systemic infections and meningitis in humans. Understanding how S. suis colonizes and interacts with its hosts is relevant for future strategies of drug and vaccine development. As with other Gram-positive bacteria, S. suis utilizes enzymes known as sortases to attach specific proteins bearing cell wall sorting signals to its surface, where they can play a role in host-pathogen interactions. The surface proteins of bacteria are often important in adhesion to and invasion of host cells. In this study, markerless in-frame deletion mutants of the housekeeping sortase srtA and the two pilus-associated sortases, srtB and srtF, were generated and their importance in S. suis infections was investigated. We found that all three of these sortases are essential to disease in pigs, concluding that their cognate-sorted proteins may also be useful in protecting pigs against infection.
Highlights
The porcine pathogen Streptococcus suis colonizes the upper respiratory tract of pigs, where it can reside as a commensal or invade and cause septicaemia, meningitis and arthritis
This signal is typically recognized by a type A housekeeping sortase, SrtA, which cleaves the protein between the T and the G amino acids of the LPXTG-like motif and transfers it to the cell surface by forming a covalent bond between the sorted protein and the peptidoglycan [11]
As cell surface proteins are often important colonization factors, here we investigated the involvement of two known sortases, the type A sortase SrtA and the type C sotase SrtF, and one putative type C sortase SrtB, in a number of S. suis phenotypes
Summary
The porcine pathogen Streptococcus suis colonizes the upper respiratory tract of pigs, where it can reside as a commensal or invade and cause septicaemia, meningitis and arthritis. The proteins attached in this way are known as sorted proteins; they encode a C-terminal cell wall sorting signal (CWSS) consisting of an LPXTG-like motif, a hydrophobic domain and a positively charged tail This signal is typically recognized by a type A housekeeping sortase, SrtA, which cleaves the protein between the T and the G amino acids of the LPXTG-like motif and transfers it to the cell surface by forming a covalent bond between the sorted protein and the peptidoglycan [11]. S. suis encodes a SrtA housekeeping sortase, the deletion of which significantly reduces the amount of protein on the cell surface of the bacteria [12] and attenuates its virulence in a piglet model of infection [13]. A srtA knockout mutant is as virulent as its parental strain in an intraperitoneal (IP) murine model of infection [14]
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