The spores are potentially anywhere or everywhere (outside a sterile environment). No need for special introduction.
"C. botulinum is prevalent in soil and marine sediments worldwide, most commonly
as spores. These spores are found everywhere. While the spores are
generally harmless, the danger can occur once the spores begin to grow out
into active bacteria and produce neurotoxins. A neurotoxin is a poisonous
chemical that affects the central nervous system. It can destroy, paralyze, or
adversely affect nerves or nerve tissue. C. botulinum produces seven different
types of neurotoxins designated by the letters A through G; only types A, B, E,
and F cause illness in humans."
