There are a lot of different ways for Bt proteins to get into our food

posted in: Syndicated | 9

The insect pest protection protein called Bt deployed in many genetically manipulated crops is hitting the news again.

Since Marcel Kuntz’ posting on the alleged detection of this protein Bt  (variety Cry1Ab) in tissues of women, including pregnant women, as claimed by Aziz Aris and Samuel Leblanc, discussion of the Aris-Leblanc scientific paper making this claim has been gaining much print-media and Internet blogger attention.

Besides doubts about whether there is any validity in the Bt detection method used to claim presence of this protein in women’s  blood and  umbilical tissues, as well discussed by Marcel Kuntz, the Aris-Leblanc paper raises a largely unanswered question of what are the sources of exposure to Bt proteins in the human diet?

It turns out that there are plenty of other sources of dietary Bt protein in addition to genetically modified crops modified to contain the protein. It is present in biopesticides used by organic farmers.

One view about this is that the Bt bacteria as a bioinsecticide by organic farmers couldn’t be a realistic source of exposure of humans to  Bt protein because the protein is unstable.

The Bt protein may in fact be unstable, but the naturally occurring bacteria that manufacture it and which are alive in the biopesticides sprayed by organic farmers are definitely not unstable. They exist as long lasting highly persistent spores in addition being able to proliferate vegetatively. Effectively they can persist hundreds of years. And in contrast to plant material containing GM-Bt, they can actively proliferate in food. Very often human diets contain these bacteria or their close relatives, and presence of Bt proteins in human bodily tissues might well be caused by exposure to these widespread non-GM sources of bacterial insecticide protein.

For example these bacteria have been found in milk samples, ice-cream, peach-juice and green-tea beverages.

Thanks to correspondent Stefan Rauschen of Aachen for reminding the Pundit of these facts of life about dietary Bt exposure. Some selected scientific literature documenting this, kindly provided by Stefan, are appended below.


Appl Environ Microbiol. 2006 May;72(5):3435-40. (
Occurrence of natural Bacillus thuringiensis contaminants and residues of Bacillus thuringiensis-based insecticides on fresh fruits and vegetables.
Frederiksen K, Rosenquist H, Jørgensen K, Wilcks A.

A total of 128 Bacillus cereus-like strains isolated from fresh fruits and vegetables for sale in retail shops in Denmark were characterized. Of these strains, 39% (50/128) were classified as Bacillus thuringiensis on the basis of their content of cry genes determined by PCR or crystal proteins visualized by microscopy. Random amplified polymorphic DNA analysis and plasmid profiling indicated that 23 of the 50 B. thuringiensis strains were of the same subtype as B. thuringiensis strains used as commercial bioinsecticides. Fourteen isolates were indistinguishable from B. thuringiensis subsp. kurstaki HD1 present in the products Dipel, Biobit, and Foray, and nine isolates grouped with B. thuringiensis subsp. aizawai present in Turex. The commercial strains were primarily isolated from samples of tomatoes, cucumbers, and peppers. A multiplex PCR method was developed to simultaneously detect all three genes in the enterotoxin hemolysin BL (HBL) and the nonhemolytic enterotoxin (NHE), respectively. This revealed that the frequency of these enterotoxin genes was higher among the strains indistinguishable from the commercial strains than among the other B. thuringiensis and B. cereus-like strains isolated from fruits and vegetables. The same was seen for a third enterotoxin, CytK. In conclusion, the present study strongly indicates that residues of B. thuringiensis-based insecticides can be found on fresh fruits and vegetables and that these are potentially enterotoxigenic.

Int J Food Microbiol. 2008 Sep 30;127(1-2):68-72. Epub 2008 Jun 12. (
The residual occurrences of Bacillus thuringiensis biopesticides in food and beverages.
Zhou G, Yan J, Dasheng Z, Zhou X, Yuan Z.

In 2006, 54 pasteurized full fat milk samples, 40 ice-cream samples, and two green-tea beverage samples were analyzed and a total of 19 Bacillus thuringiensis-like strains were isolated, nine from seven pasteurized milks, one from an ice-cream with peach pulp and juice, and nine from two green-tea beverages. These strains were classified as B. thuringiensis, contained the cry1A gene and produced crystal inclusions during sporulation. All strains were characterized by a serotyping test, SDS-PAGE, random amplified polymorphic DNA, and enterotoxic gene PCR analysis. Most isolates produced bipyramidal crystals and belonged to serotypes H3a3b, H5a5b, or H7. Furthermore, two strains from pasteurized full fat milks and three strains from green-tea beverages were indistinguishable from the B. thuringiensis subsp. kurstaki strains isolated from commercial biopesticides (Kaiyan, Qiangdi, Lvpuan and Sutai), suggesting the residual occurrences of B. thuringiensis from biopesticides in food and beverages.

Appl Environ Microbiol. 2001 Mar;67(3):1035-43. (
Identification of Bacillus thuringiensis subsp. kurstaki strain HD1-Like bacteria from environmental and human samples after aerial spraying of Victoria, British Columbia, Canada, with Foray 48B.
Valadares De Amorim G, Whittome B, Shore B, Levin DB.

Aerial applications of Foray 48B, which contains Bacillus thuringiensis strain HD1, were carried out on 9 to 10 May, 19 to 21 May, and 8 to 9 June 1999 to control European gypsy moth (Lymantria dispar) populations in Victoria, British Columbia, Canada. A major assessment of the health impact of B. thuringiensis subsp. kurstaki was conducted by the Office of the Medical Health Officer of the Capital Health Region during this period. Environmental (air and water) and human (nasal swab) samples, collected before and after aerial applications of Foray 48B, both in the spray zone and outside of the spray zone, were analyzed for the presence of strain HD1-like bacteria. Random amplified polymorphic DNA analysis, cry gene-specific PCR, and dot blot DNA hybridization techniques were used to screen over 11,000 isolates of bacteria. We identified bacteria with genetic patterns consistent with those of B. thuringiensis subsp. kurstaki HD1 in 9,102 of 10,659 (85.4%) isolates obtained from the air samples, 13 of 440 (2.9%) isolates obtained from the water samples, and 131 of 171 (76.6%) isolates from the nasal swab samples. These analyses suggest that B. thuringiensis subsp. kurstaki HD1-like bacteria were present both in the environment and in the human population of Victoria prior to aerial applications of Foray 48B. The presence of B. thuringiensis subsp. kurstaki HD1-like bacteria in human nasal passages increased significantly after the application of Foray 48B, both inside and outside the spray zone.

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David Tribe is an applied geneticist, teaching graduate/undergrad courses in food science, food safety, biotechnology and microbiology at the University of Melbourne.