Gangrene?

 
A very friendly stray that we feed had a cut.  We saw him yesterday and his face and head have turned black and looks terrible.  We are trying to catch him to take him to a vet.  From past experience he is very friendly and likes to be petted but he scratched me last year when we tried to get him into a cat carrier.  He obviously has a very severe infection and we are trying to catch him, but do we need to take extra precautions because of this black area we think might be gangrene?  Any suggestions on getting him into a cat carrier?. 

Get a live trap and use that to transport him in to the vet.

The gangrene is not actively contagious. The bacteria doesnt like air.  That said, you dont want these bacteria put into you. So use protective gloves and thick clothes.  Wrap him up with something, a big thick towel or so.  Wrapped up he wont fight.  Throw the towel on him perhaps.  (you can train on a dummy at first, or even on your own cat).

A trap is of course best.  Possibly he may even himself go into the carrier, being sick he perhaps understands he needs help. This happens.

Another question is, If it is gangrene, what can be done?  The most common is amputating, but head and face? Can he be helped with massive antibiotica treatment?

Phone a vet and ask.

If the vet is pessimistic:

Possibly the most kind is not waiting for the vet to pts him, but spare him the stress and time of suffering. Do you have a neigbour who is a experienced hunter and knows how to do?

Good luck!   *vibes*

If it is gangrene - deep wound infection because as was already mentioned those bacteria only grow in absence of air / oxygen - it stinks like rotting meat.

Is it possible that what you are seeing are just massive scabs from surface scrapes?

Regardless, he needs to see a vet as soon as you can get him there. Good luck!