If you take the lens and shoot with it everyday, the ever-present spores will not have a chance to take hold and grow. Or just gently work the lens aka zoom in and out and focus focus every day or alternate days and it will not likely grow.
You will hear of photographers who use their equipment every single day, and fungus has not grown for years.
I don't think any of us study mold, but here's something for you to read.
How long does it take mold to grow?
To be more specific, we should ask, "How long does it take for a mold spore to germinate?" Then we should ask, "How long does it take growing mold to colonize?"
To grow, molds need a food source, a certain temperature and moisture. Where these conditions are present, molds can germinate and colonize. How fast growth occurs depends on the combination of conditions. Spores can germinate after only 12 hours in some conditions and some grow in 24 to 48 hours. Houses offer an ample food supply — drywall, wood, insulation, paper. When these materials become damp or wet, settled spores can become growing molds.
Molds may colonize in 1 to 12 days depending on the type of mold. Following are several types of molds and the number of days in which colonization may take place:
* Mucor sp. colonizes between 1 and 2 days.
* Rhizopus sp. colonizes between 1 and 2 days.
* Aspergillus sp. colonizes between 2 and 3 days.
* Penicillium sp. colonizes between 2 and 3 days.
* Stachybotrys chartarum colonizes between 8 and 12 days.