Pasteurella species are part of the normal oral flora of cats. You can come in contact with it, through fecal-oral, or infected secretions, and through the air provided the cat has sneezed. Its because of this they tend to tell women to not clean kitty litter when pregnant. Now with all this said, it is an opportunistic pathogen generally problems only arise if another animal ie) rat, has a respiratory infection, is stressed etc. Not to say a seemingly healthy rat cannot be effected but it's far less likely. I have a cat, and she sleeps on the rat cage, and spends most of her days interacting with them because she loves them. Even at the end of two of my rats lives when they both had tumors and other issues, they never had a decline in respiratory, even though one was an occasional sneezer. Not to say that they didn't get pasteurella, and that your's won't, but I feel even being careful with washing procedures etc, your rats have or will probably come in contact with it. I'm by no means an expert on the subject..just my two cents.
Also pregnant women shouldn't clean litter boxes due to Toxoplasmosis, which is a bigger risk. It also alters the brain circuitry in rats ( and mice) and can make them lose the fear of cats as well as make them aroused towards the cat.
thought I should add that.