"Yes. Apparently, a different Kihara brought in some kind of mold used for combat and this Kihara Enshuu is trying to use it. By causing artificial changes to it, she is increasing its infectiousness and toxicity and then will spread it as a biological weapon."

[...]

Microscopic life forms underwent changes to their genetic structure due to external causes relatively easily.
However, making changes to the parts you wanted in order to produce the effects you wanted was decidedly more difficult.

Kumokawa Maria brought her hand to her jaw and said, "But mold is a living thing. It needs heat to remain active. It seems like bringing down the temperature to make us suffer would run counter to this."

"She is killing anyone she can by dropping the temperature. She will only spread the mold once the heat has gone back up enough for it to be active. That way, she can kill as many people as possible. Mold in the bath can be quite persistent. The same goes for athlete's foot. It stops being active in a difficult environment, but that does not kill it. After hibernating for a long period of time, it can reactivate once the environment is more favorable."

"But Baggage City doesn't have any specialized microbe research facilities. At least none it advertised. Unless some new conspiracy shows itself, I would assume she is going to misuse a civilian facility."

"That's exactly right. It seems Kihara Enshuu is headed for the plant factory. Y'know, those container shaped things. It's a new type of field that grows vegetables by using light with a special wavelength to induce photosynthesis, conditions the air to keep the temperature right, and soaks the roots in nutrients. Using it, you can pick the crops about thirty times in a year."

[...]

"Very bad," she replied simply. "By the way, if you don't even have that kind of fundamental knowledge on the subject, how could you tell what Kihara Enshuu is planning? You don't seem to have what it takes to build up to that conclusion."

"Oh, to be honest, I was given this advice by someone else."

"Who?"

"A man wearing a helmet and a coat."

Toaru Majutsu no Index New Testament Vol.4 sub.26