The humidity of the machine combined with washing salts is merciless to cutting edges and carbon-containing steel in general. Wash them by hand, taking care not to use the abrasive side of the sponge which would scratch the blades. However, if your knives end up in the machine by mistake, take them out at the end of the program and dry them.
Remember to sharpen them regularly (for example with the sharpener from Lansky "Pocket ceramic sharpening/sharpening system" : it sits on your work surface and will always be within reach. Its use is simple and you will give a perfect edge).