Earth DNA deposited on Titan by Huygens?

Please excuse this naive query:

How is it possible to know that we have not just deposited some "earth
DNA" on Titan, via a single (or multiple) viral or bacterial
hitchhiker?

I realize that clean rooms are used for vehicle and instrument
fabrication, that heat of atmospheric entry, the 7 year transit time
and the radiological environment of interplanetary space all mitigate
against this possibility, but...

One compromised bacterium?
One (or a dozen, or a few hundred) virus/viruses?

And could someone point me to a discussion of this?
(Fresher than the period of manned lunar exploration.)

And is this now considered a trivial concern in the world of planetary
exploration?


Many thanks...