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Hernandez-Mendoza et al (2009) Key role of teichoic acids on aflatoxin B1-binding by probiotic bacteria

Hernandez-Mendoza et al (2009) Key role of teichoic acids on aflatoxin B1-binding by probiotic bacteria

Citation

Hernandez-Mendoza A, Guzman-de-Pena D and Garcia HS (2009). Key role of teichoic acids on aflatoxin B1-binding by probiotic bacteria. Journal of Applied Microbiology 47(6):1064-8.

Objective

To investigate the ability of five probiotic strains to bind with aflatoxin B1 (AFB1), and the role of cell wall teichoic acids in this process.

[Explanatory note: aflatoxins are fungal metabolites that can contaminate a range of food, including grains, peanuts, tree nuts and beans due to the growth of certain Aspergillus spp. AFB1 is considered a potent carcinogen. Teichoic acids are found in the cell wall of Gram-positive bacteria.]

Methods

The probiotic strains selected for this in vitro investigation were Lactobacillus reuteri NRRL14171 (Lr), Bifidobacterium bifidum NCFB2715, Lactobacillus casei Shirota (LcS), Lactobacillus johnsonii NCC533 and Lactobacillus casei defensis DN-114-001. An initial binding assay was conducted, in which live probiotic cells were added to an aqueous solution containing AFB1. The stability of the bacterial–mycotoxin complexes were assessed by repeated washes with phosphate-buffered saline solution.

On the basis of this test, two strains were chosen for further investigations using different cell preparations:

  • protoplasts (cell wall completely removed)
  • spheroplasts (cell wall partially removed)
  • exopolysaccharide extracts
  • bacterial cell wall fragments
  • teichoic acid-deficient bacteria
  • bacteria treated with polycation (to disrupt the outer membrane)
 

Results

All five probiotic strains were able to bind to the aflatoxin but with varying degrees of affinity. LcS and Lr demonstrated the greatest binding affinity (67% and 79% respectively) after four hours of incubation. These also formed significantly more stable bacteria-mycotoxin complexes stability during incubation (P

AFB1 binding was influenced by pH; at pH7.2 LcS and Lr showed the greatest binding capacity after 4 hours incubation with the aflatoxin.

The percentage of aflatoxin bound to the treated bacterial cells (i.e. protoplasts, spheroplasts, teichoic acid-deficient bacteria, bacteria treated with polycations and exopolysaccharide extracts) was significantly lower than the percentage bound to viable whole bacterial cells.

Bacterial cell wall fragments, however, demonstrated a binding capacity comparable to that seen with viable cells of LcS and Lr, at 68% and 62% respectively.

Conclusions

This study gave new information about AFB1 binding by probiotic strains, which supports the theory that certain probiotics could prevent absorption of carcinogenic aflatoxin from the gastrointestinal tract.

The results suggest that cell wall integrity is important for aflatoxin binding, and that teichoic acid components of LcS and Lr are involved in this process.

 
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