What process has an exclusive open on the USB port?

I can't get any Android device to work with ADB on my Macbook Pro (2015 model, running 10.11.4). When I execute the following command,

adb kill-server ; adb devices

I get the following output

List of devices attached

* daemon not running. starting it now on port 5037 *

adb I 2192 55546 usb_osx.cpp:259] Found vid=18d1 pid=4ee2 serial=8XXXXXXXXXXXXXXX

adb I 2192 55546 usb_osx.cpp:259]

adb E 2192 55546 usb_osx.cpp:331] Could not open interface: e00002c5

adb E 2192 55546 usb_osx.cpp:265] Could not find device interface

* daemon started successfully *

The 8XXXXXXXXXXXXXXX is the serial number of my phone, it's getting that far with it. The OS sees the phone and the Android File Transfer app can see the folders on it. This happens with any physical Android device (emulators connect just fine). I looked at the ADB source code and that error message occurs when ADB tries to open a connection to the USB port. Different phones, different cables, rebooting, reinstalling Android SDK, no effect on the problem.

If I boot my Mac in safe mode, I can connect via ADB. It sounds like some other app or service is interfering with ADB. Has anyone come across this before? Is there any way that I can see if another process is blocking ADB from connecting? Is there a way to get a list of processes that have opened the USB ports?