Efficient utilization of complex N-linked glycans is a selective advantage for Bacteroides fragilis in extraintestinal infections

Abstract

Bacteroides fragilis is the most common anaerobe isolated from clinical infections, and in this report we demonstrate a characteristic of the species that is critical to their success as an opportunistic pathogen. Among the Bacteroides spp. in the gut, B. fragilis has the unique ability of efficiently harvesting complex N-linked glycans from the glycoproteins common to serum and serous fluid. This activity is mediated by an outer membrane protein complex designated as Don. Using the abundant serum glycoprotein transferrin as a model, it has been shown that B. fragilis alone can rapidly and efficiently deglycosylate this protein in vitro and that transferrin glycans can provide the sole source of carbon and energy for growth in defined media. We then showed that transferrin deglycosylation occurs in vivo when B. fragilis is propagated in the rat tissue cage model of extraintestinal growth, and that this ability provides a competitive advantage in vivo over strains lacking the don locus.

Dps and DpsL Mediate SurvivalIn VitroandIn Vivoduring the Prolonged Oxidative Stress Response in Bacteroides fragilis

“…These data also indicate that Dps and DpsL may play overlapping roles in protecting the cells from oxidative stress damage in vivo, because the absence of both was required to see the phenotype. As previously shown in this model, B. fragilis reaches high cell numbers and then enters a stationary-like phase where the high cell density is maintained (8,31). Interestingly, on day 1 the ⌬dps ⌬bfr mutant was able to compete effectively with the wild type and was close to 50% of the 10 8 to 10 9 CFU/ml; however, on days 4 and 8, there was a decrease in the competitive ability of the double mutant (Fig.…”

“…Factors that contribute to B. fragilis survival within the abscess are poorly understood. In a previous study using the rat tissue cage model, in vivo microarray analysis demonstrated that the don locus was highly expressed in the infected tissue cages and was required for maximum survival in vivo (31). We reexamined these microarray data and found that there was a 4-to 6-fold increase in expression of dps and bfr, suggesting that Dps and DpsL may promote survival within the abscess.…”

“…This model has effectively been used to show the attenuation of mutant strains of B. fragilis within an artificial abscess (8,31). Experiments that compared the ability of the wild-type strain to outcompete single ⌬dps and ⌬bfr mutants showed only slight attenuation that was not statistically significant.…”

“…During this time, the ball becomes encapsulated in connective tissue, the tissue becomes vascularized, and the ball fills with sterile serous fluid (ϳ25 ml per ball). Competition assays were performed in this model as previously described (31). In brief, overnight cultures were diluted in PBS (50 mM sodium phosphate, 150 mM sodium chloride [pH 7.4]) and mixed in a 1:1 ratio of wild type (IB-101) to mutant (⌬dps, ⌬bfr, or ⌬dps ⌬bfr) to a total of 1 ϫ 10 5 CFU/ml as a standard inoculum.…”

cis -Encoded Small RNAs, a Conserved Mechanism for Repression of Polysaccharide Utilization in Bacteroides

“…This can lead to peritonitis, intra-abdominal abscess, and bacteremia (9, 10). The dominance of B. fragilis in these infections can be attributed to an array of virulence factors that include polysaccharide capsule phase variation, a striking resistance to oxidative stress, and the ability to exploit novel host nutrient sources (11)(12)(13)(14).The ability to effectively compete for limited nutrients is essential for Bacteroides colonization in the gut as well as for success in extraintestinal infections. The key element of nutrient acquisition is the presence of a family of outer membrane protein complexes dedicated to the uptake and catabolism of polysaccharides (15)(16)(17).…”