This is how I spend most Monday mornings - cleaning microphones after a big weekend. I would assume that all hire companies do the same. You would be surprised what gets left behind in mics - some of it you can see, but most you can't! So this is how I make sure all our mics are totally kept clean and germ free as much as possible:
1. Unscrew the head of the mic and remove the inner foam from the grille
2. Wash both in warm water with disinfectant
3. An old toothbrush is ideal to clean the inside of the metal grille
4. Wipe the outside of the mic itself with a disinfectant towelette
5. Lay all out on a clean towel to dry.
Note, it's important to not replace the foam until it is completely dry as this could cause rusting of the grille. You can always use a hair dryer to hurry up the process.
If you are at a gig and have multiple users of main mics on the night, why not take a moment back stage to give a light misting to the mic grille between performers with Geln 20 . If they happen to see you doing this, they are always impressed so try and keep your act clean!
Why not keep some disinfectant wipes and Glen 20 back stage in case of emergencies.