To add to Ruth's explanation ... a fungal organism is not a bacteria ... they are two different things.
Fungal infections of the fingernails are in fact very rare indeed ... the conditions in which they like to live are simply not normally present on hands.
A bacteria makes its presence known when you can see the staining between the enhancement and the natural nail. Colouration varies from light green through to black depending on the severity of the infection and how long it has been present with no treatment. When the enhancement is removed, the bacteria ceases to thrive ... if the infection is not severe, the plate can be cleaned and the enhancement reapplied.
The stain will have to grow out. A Dr's advice is not normally needed.
Feet on the other hand, which are encased most of the time in the warm damp environment Ruth describes, are in the perfect environment to grow and thrive. A fungal infection is typically located under the natural nailplate and causes onycholysis of the plate as well. A fungal infection can be characterized by a white, crusty appearance at the hyponychium ... smells cheesy ... and generally looks 'active'. Very difficult to get rid of. Dr's help should be advised.