Identification of Genes Preferentially Expressed by Highly Virulent Piscine Streptococcus agalactiae upon Interaction with Macrophages

Abstract

Streptococcus agalactiae, long recognized as a mammalian pathogen, is an emerging concern with regard to fish. In this study, we used a mouse model and in vitro cell infection to evaluate the pathogenetic characteristics of S. agalactiae GD201008-001, isolated from tilapia in China. This bacterium was found to be highly virulent and capable of inducing brain damage by migrating into the brain by crossing the blood–brain barrier (BBB). The phagocytosis assays indicated that this bacterium could be internalized by murine macrophages and survive intracellularly for more than 24 h, inducing injury to macrophages. Further, selective capture of transcribed sequences (SCOTS) was used to investigate microbial gene expression associated with intracellular survival. This positive cDNA selection technique identified 60 distinct genes that could be characterized into 6 functional categories. More than 50% of the differentially expressed genes were involved in metabolic adaptation. Some genes have previously been described as associated with virulence in other bacteria, and four showed no significant similarities to any other previously described genes. This study constitutes the first step in further gene expression analyses that will lead to a better understanding of the molecular mechanisms used by S. agalactiae to survive in macrophages and to cross the BBB.

Two Novel Functions of Hyaluronidase from Streptococcus agalactiae Are Enhanced Intracellular Survival and Inhibition of Proinflammatory Cytokine Expression

“…The ability to sense the environment and mount an appropriate adaptive transcriptional response may be of crucial importance for S. agalactiae colonization and pathogenicity. Our previous study showed that the expression of hylB was upregulated by the interaction of S. agalactiae with murine macrophages (14). The present study demonstrated that inactivation of hylB reduced the numbers of intracellular viable S. agalactiae cells (Fig.…”

“…Female BALB/c mice (5 to 7 weeks of age) were purchased from the Experimental Animal Center, Yangzhou University. Previous studies had shown that the bacterial strain GD201008-001 was highly virulent to BALB/c mice by intraperitoneal administration, with LD 50 values of less than 10 CFU (14). The mice infected with a predetermined dose of 5 ϫ 10 2 CFU (50-fold greater than the LD 50 in mice infected with the GD201008-001 wild-type strain) of the wild-type, mutant, and complemented strains.…”

“…Our previous study observed that expression of the hylB gene that encodes the S. agalactiae hyaluronidase (Hyl) was upregulated through interaction with murine macrophages in a selective capture of transcribed sequences (SCOTS) approach (14). Hyaluronidase (Hyl) is an endoglycosidase that cleaves glycosaminoglycan chains, thereby degrading hyaluronic acid (HA) (15).…”

Identification of Aeromonas hydrophila Genes Preferentially Expressed after Phagocytosis by Tetrahymena and Involvement of Methionine Sulfoxide Reductases

“…Bacterial transcripts were then separated from host cDNA by SCOTS as described previously (Guo et al, 2014). Briefly, denatured, biotinylated, and sonicated A. hydrophila genomic DNA (gDNA) fragments (0.6 μg) were mixed with 5 μg of sonicated ribosomal DNA (from plasmid pMD18-T16S, pMD18-T23S1, and pMD18-T23S2) to pre-block rRNA encoding regions on the gDNA.…”

Modification of the CpsA Protein Reveals a Role in Alteration of the Streptococcus agalactiae Cell Envelope

“…Group B Streptococcus (GBS), Streptococcus agalactiae, can colonize the human vaginal and rectal mucosa as a commensal organism (1-3) but can also cause a range of invasive infections in immunocompromised and older adults (4)(5)(6). GBS is also a broad-host-range pathogen capable of causing severe sepsis and meningoencephalitis in fish (7)(8)(9)(10)(11)(12), bovine mastitis (13)(14)(15), and human neonatal sepsis and meningitis (16)(17)(18)(19)(20)(21) and has been recently implicated in chorioamniosis (22,23), causing premature birth (24,25) and stillbirth (25,26). The current strategy to prevent GBS infection of neonates is intrapartum antibiotic prophylaxis (IAP) (27), i.e., intravenous antibiotics given to a woman during labor and delivery.…”