I mean, if you make an infusion you have to boil the water, so you have to wait untill the infusion gets the same temperature there is in the salamandra's room.
Echinacea is an american product, you can find information here:
http://en.wikipedia.org/wiki/Echinacea
I have many articles that show the benefits of using echinacea on amphibians and reptiles, it is widely used with turtles. Unfortunately I haven't find any in english. I have use it myself with a group of young taricha granulosa with very good results.
Maybe herbalist's is not a good translation. I mean the kind of pharmacy where you can find products that don't need medical prescription such as diet product, natural medicine, etc. In almost all of them you can buy echinacea as it is a very popular remedy against infections. May be you know it for something like American cone flower, black Susan, black Sampson, comb flower, hedgehog, Indian head, Kansas snakeroot, narrow-leaved purple coneflower, scurvy root, or snakeroot.
I am talking about a natural product, as I don,t see your salamander seriously ill. They show a good apetite and the infection doesn't affect a large area. Obviously a sulfa cream is a powerfull and faster remedy. Anyway I would use the echinacea even if you use the cream, to boost the inmune system.