Arduino Leonardo (ATMEGA 32U4) not detected on OS X El Capitan 10.11.0

I've just installed OS X El Capitan 10.11.0 final (no Beta Version). Unfortunately, there is a strange Issue: The Arduino Leonardo is not detected anymore in the Arduino IDE (1.6.5r5). Other Arduino models with USB to serial transmitters (FTDI etc.) are not affected.

The device is listed in "About this Mac, USB", but it does not show up in the /dev folder, if I'm entering the following commands:

cd /dev
ls

Any thoughts?

Thanks for your hints!