Surface structures, haemagglutination and cell surface hydrophobicity of Bacteroides fragilis strains

Abstract

Nineteen strains of Bacteroides fvagils were examined by negative staining for surface structures. One strain (ATCC 23745) possessed peritrichous fibrils, 16 strains carried peritrichous fimbriae and two strains carried no surface structures. The fimbriae had a diameter of 2-1 & 0.25 nm and appeared to be 'curly'. Only a small proportion (4 to 41%, depending on the strain) of cells in a population carried fimbriae or fibrils. Strain A312 showed phase variation of fimbriae as expression of fimbriae was repressed at 20 "C and in early exponential phase at 37 OC. The fibrils on strain ATCC 23745 did not exhibit phase variation in response to changes in incubation temperature, growth phase or growth in two different media. Capsules were demonstrated by the Indian ink method on 18 of the 19 strains, varying in size from strain to strain and within the same population. Cultures often contained both capsulate and noncapsulate cells. All strains possessed an electron dense ruthenium red staining layer between 7.9 and 23.9 nm in width attached to the outer membrane. Cell surface hydrophobicity quantified by the hexadecane partition assay gave low values ranging from 6.6 to 52.1%. Only a few strains were able to haemagglutinate and these were only weakly active. There was no correlation between cell surface hydrophobicity, haemagglutinating activity and surface structures.

A study of the candidate virulence factors of Bacteroides fragilis

“…All B.fragifis strains examined possessed a capsule, the capsule size varying between strains ; both capsulated and noncapsulated cells were present in populations of all strains. The same observation has been reported by other investigators (Patrick et al, 1986;Oyston & Handley, 1990). Since the avirulent strains also possessed a capsule, the documented importance of a capsule for the virulence of B. fragilis (Kasper, 1976) was not confirmed in this study.…”

“…Vel et al (1986) and Oyston & Handley (1990) detected different patterns of haemagglutination among their B. fragilis strains. Such differences were not obvious in this study, but we only studied five virulent strains.…”

“…Human 0, horse, sheep, guinea pig and chicken blood were collected each week and stored at 10% (v/v) concentration in Alsever's solution (Oyston & Handley, 1990) at 4 "C. Erythrocytes were washed three times with PBS and suspended in PBS to give a concentration of 2% (v/v). Bacterial cultures were grown for 24 h then washed three times in PBS and suspended in PBS to a concentration of about 2.5 x lo9 bacteria ml-l, as estimated by optical density.…”

Virulence markers and antimicrobial susceptibility of bacteria of the Bacteroides fragilis group isolated from stool of children with diarrhea in São Paulo, Brazil

“…The capsular polysaccharide B. fragilis acts as a protector against neutrophil phagocytes and the complement bactericidal activity; it can produce abscesses in animals (Lindberg & Weintraub 1985). Moreover, all the tested strains showed characteristics such as β-hemolytic, hydrophilic, and human or horse serum resistant, in accordance with Rotimi and Eke (1984), Oyston and Handley (1990), and Namavar et al (1991).…”

Bacteroides: the Good, the Bad, and the Nitty-Gritty

“…In various studies, pili have also been implicated in hemagglutination and adhesion (51,193). Other studies, however, implicated the polysaccharide capsule rather than the protein appendages (177). Recent functional genomic studies classifying databases of specific molecules note that members of the Bacteroides secrete large numbers of lipoproteins with an N-terminal beta-propeller domain, which may form a specialized adhesion module (7,20).…”