Preliminary safety evaluation of a new Bacteroides xylanisolvens isolate

Abstract

Besides conferring some health benefit to the host, a bacterial strain must present an unambiguous safety status to be considered a probiotic. We here present the preliminary safety evaluation of a new Bacteroides xylanisolvens strain (DSM 23964) isolated from human feces. First results suggest that it may be able to provide probiotic health benefits. Its identity was confirmed by biochemical analysis, by sequencing of its 16S rRNA genes, and by DNA-DNA hybridization. Virulence determinants known to occur in the genus Bacteroides, such the bft enterotoxin and other enzymatic activities involved in the degradation of the extracellular matrix and the capsular polysaccharide PS A, were absent in this strain. The investigation of the antibiotic susceptibility indicated that strain DSM 23964 was sensitive to metronidazole, meropenem agents, and clindamycin. Resistance to penicillin and ampicillin was identified to be conferred by the β-lactamase cepA gene and could therefore be restored by adding β-lactamase inhibitors. The localization of the cepA gene in the genome of strain DSM 23964 and the absence of detectable plasmids further suggest that a transfer of β-lactamase activity or the acquisition of other antibiotic resistances are highly improbable. Taken together, the presented data indicate that the strain B. xylanisolvens DSM 23964 has no virulence potential. Since it also resists the action of gastric enzymes and low-pH conditions, this strain is an interesting candidate for further investigation of its safety and potential health-promoting properties.

Fig 1

Phylogenetic representation and RAPD profile of B. xylanisolvens DSM 23964. (A) Phylogenetic representation of different Bacteroides strains based on 16S rRNA gene sequences. The scale bar represents 0.01 substitutions per nucleotide position. Bootstrap values (>50%) based on 1,000 replications are listed as percentages at branching points. (B) RAPD amplification profile with primer OPX-14. Lanes: 1 and 5, 1-kb DNA ladder (Bioline); 2, B. xylanisolvens DSM 23964; 3, B. xylanisolvens DSM 18836; 4, negative control (water).

Fig 2

Molecular analysis of the binding of strain DSM 23964 to Caco-2 cells. (A) GAPDH and sucrose isomaltase. Lanes: 1, 100-bp DNA ladder (Bioline); 2, first day; 3, third day; 4, sixth day; 5, eighth day; 6, 10th day; 7, 13th day; 8, 14th day, 9, negative control. (B) Detection of strains B. xylanisolvens DSM 23964 and B. fragilis DSM 1396. Lanes: 1, 100-bp DNA ladder; 2, B. xylanisolvens DSM 23964 after first wash step; 3, B. xylanisolvens DSM 23964 after sixth wash step; 4, B. xylanisolvens DSM 23964 + Caco-2 cells; 5, B. fragilis DSM 1396 after first wash step; 6, B. fragilis DSM 1396 after sixth wash step; 7, B. fragilis DSM 1396 + Caco-2 cells; 8, Caco-2 cells; 9, strain DSM 23964; 10, B. fragilis DSM 1396; 11, negative control. (C) Detection of L. acidophilus. Lanes: 1, L. acidophilus DSM 9126 after first wash step; 2, L. acidophilus DSM 9126 after sixth wash step; 3, L. acidophilus DSM 9126 + Caco-2 cells; 4, Caco-2 cells; 5, L. acidophilus DSM 9126; 6, negative control; 7, 100-bp DNA ladder.