Final answer:
Bacillus thuringiensis (Bt) is non-pathogenic to humans because its toxin, Bt toxin, is specific to the alkaline digestive systems of insects and does not affect the acidic digestive systems of humans.
Step-by-step explanation:
Bacillus thuringiensis, commonly referred to as Bt, is non-pathogenic to humans because it specifically targets insects. This bacterium produces protein crystals during sporulation that are toxic to certain insect species. These toxins, known as Bt toxins, must be ingested by insects to become activated. Once inside the insect's intestines, the toxin disrupts their digestive processes, leading to starvation and death within a couple of days.
The reason why Bt toxin is not harmful to humans lies in the specific way the toxin works; it is designed to act on the alkaline digestive systems of insects, which differ significantly from the acidic digestive systems of humans and other mammals. In addition, the specific receptors that Bt toxin binds to are not present in human gut cells.
The safety and eco-friendliness of Bt toxin has led to its widespread use as a natural insecticide by organic farmers. Additionally, biotechnological advancements have enabled the cloning of the crystal toxin genes from B. thuringiensis to be introduced into plants. This allows for plants to produce their own Bt toxin, providing them with in-built protection against insect pests, which reduces the need for synthetic pesticides.
However, the potential transfer of genes for antibiotic resistance, for example, from Bt to pathogenic bacterium via transduction, is a hypothetical concern. This could hypothetically occur if a nonpathogenic bacterium like Bt were to transfer its antibiotic resistance genes to a pathogenic bacterium, potentially leading to more antibiotic-resistant infections.