Bacillus Thuringiensis
Bacillus thuringiensis (B. thuringiensis) is a gram positive, facultative anaerobic microbe that is found in the soil.1 It is used as an alternative to chemical pesticides because it produces toxins that kill insect larvae.1 It has been found that different strains of B. thuringiensis are toxic to specific species of insects.1
Mechanism of Action
B. thuringiensis produces endotoxins that are eaten by insect larvae. In the susceptible larvae’s gut, the endotoxin is activated by proteolysis which causes structural changes to the cell wall through the creation of pores.2 These pores affect membrane integrity by creating an osmotic imbalance which leads to cell death.2 Another mechanism involves the endotoxin binding to a specific receptor in the membrane which stimulates cell death.2 Both mechanisms cause the gut to become paralyzed, and the insect larvae will stop eating and ultimately starve.2 Figure 1 shows a depiction of the mechanism of action of B. thuringiensis.
Biotransformation and Toxicokinetics in Humans
In some instances, food and potable water may become contaminated with B. thuringiensis through agricultural uses. It can also be inhaled if aerosolized.3
If B. thuringiensis is eaten:
B. thuringiensis does not travel from the gut or reproduce. Any toxin that may be produced is broken down via normal processes in the gut. B. thuringiensis is usually eliminated from the body in approximately 2-3 days.3
If B. thuringiensis is inhaled:
Wherever B. thuringiensis ends up in our bodies through inhalation (lungs, kidneys, lymph, blood), our immune system will get rid of it. B. thuringiensis is usually eliminated from the body in approximately 1 day.3
Target Organs
Humans3
Gastrointestinal tract (eating)
Lungs/nose/throat (inhalation)
Skin/eyes (touching)
Larvae3
Gastrointestinal tract (eating)
What might be signs and symptoms of B. thuringiensis exposure?
Luckily, from available evidence, B. thuringiensis does not seem to be toxic to humans. There have been some studies in rats and humans that showed the following potential symptoms of exposure:3
- Eye irritation
- Skin irritation
- Nasal irritation
- Throat irritation
- Difficulty with sleep and concentration
- Stomach upset
- Potential development of skin allergies if exposed for long periods of time (greater than four months)
Is B. thuringiensis carcinogenic to humans?
Currently, there is no evidence that B. thuringiensis is carcinogenic to humans.3
Genetic Susceptibility or Heritable Traits
There are no known genetic predispositions or heritable traits that may make humans more susceptible to B. thuringiensis. However, genetic variability within an insect species may alter its susceptibility. A study showed that isolated B. thuringiensis strains from Latin American soil had variable toxicity against Spodoptera frugiperda populations from Mexico, Brazil and Columbia.4
Historical Exposures
In the early 1900s, the silkworm was an economically important insect. B. thuringiensis was first isolated in 1901 from an infected silkworm larvae in Japan. Later, B. thuringiensis was isolated from four moth larvae in Thuringia, a province in Germany, thus providing the origin of the name Bacillus thuringiensis.5
Treatment
Infection from B. thuringiensis is quite rare. If infection does occur, antibiotics can be used as treatment.5
Biomarker
XRE, a transcriptional regulator, was found to be an effective biomarker when using real-time PCR (polymerase chain reaction) in differentiating between Bacillus cereus groups and B. thuringiensis.6 The study concluded that XRE can be a useful biomarker in effectively identifying B. thuringiensis in food.6
If you enjoyed learning about B. thuringiensis, check out this video from the National Pesticide Information Center!
References:
1. World Health Organization. Environmental Health Criteria 217: Microbial Pest Control Agent: Bacillus Thuringiensis. Updated 1999. Retrieved from https://www.who.int/ipcs/publications/ehc/en/EHC217.PDF.
2. Luiz de Almeida Melo, A, Soccol, VT, Soccol, CR. (2016). Bacillus thuringiensis: mechanism of action, resistance, and new applications: a review. Crit Rev Biotechnol. 36(2):317-26. doi:10.3109/07388551.2014.960793.
3. Perez, J.; Bond, C.; Buhl, K.; Stone, D. 2015. Bacillus thuringiensis (Bt) General Fact Sheet; National Pesticide Information Center, Oregon State University Extension Services. http://npic.orst.edu/factsheets/btgen.html
4. Monnerat, R, Martins, E, Queiroz, P, et al. (2006). Genetic variability of Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) populations from Latin America is associated with variations in susceptibility to Bacillus thuringiensis cry toxins. Appl Environ Microbiol.72(11):7029-35. doi: 10.1128/AEM.01454-06.
5. Ehling-Schulz, M, Koehler, TM, Lereclus, D. (2019). The Bacillus cereus Group: Bacillus species with Pathogenic Potential. Microbiol Spectr. 7(3):10.1128/microbiolspec.GPP3-0032-2018. doi: 10.1128/microbiolspec.GPP3-0032-2018.
6. Wei, S, Chelliah, R, Park, B-J, et.al. (2019). Differentiation of Bacillus thuringiensis From Bacillus cereus Group Using a Unique Marker Based on Real-Time PCR. Front Microbiol. 2019; 10: 883. doi: 10.3389/fmicb.2019.00883.