Worries for a bacterial infection on 3 orchids

[Viperalus]

On the 30th of December I received three orchids that came from a seller in the same package. Now, I have noticed yellow leaves and brown spots on these three orchids and I am worrying that they might be a bacterial infection. A week ago the leaves of both Bulbophyllums were green with no spots and now they are like you see in the photos.

As about the Bifrenaria aureo-fulva, there were some small brown spots when I received it on 30th of December as you can see at the photo below:



You can see all the photos of the orchids at this link. By pressing the tab "all sizes" you can view larger images.
You can view them also at the Slideshow if you find it difficult to browse to the other images.

I worry that it maybe could spread to all the other orchids that I have. I keep them all together and very close to each other, yet the Burrageara Nelly Isler doesn't seemed affected (not at all brown spots and/or yellow leaves). And she is next to the Bulbophyllum dearei.