Inside residential house service panels, I often see the neutral bus is bonded to enclosure( bya metal strip or by a brass screw), I can see Grounding bus screw to the enclosure. However, I rarely see the neutral bus is bonded directly to the grounding bus , such as by a wire,
They have a choice.
If the main service panel happens to be the same place that the grounded neutral conductor to the grounding electrode or EGC, which you will follow back to the earth bond, then there is no problem mixing grounds and neutrals on the same bus bar (as long as there is an appropriate number of conductors terminated under each lug which appears to be the case, except for several twisted ground conductors under one lug.
The equipment grounding bus is permitted to be bonded to the cabinet by the mounting screws and the metal enclosure is permitted to be part of the fault current path. No wire connection is required between the EG bus and another EG bus or the neutral bus. The connection of the EGC to the neutral is via the main bonding jumper (MBJ) which is typically a screw or a strap.
Yes that’s it Larry. 
Excellent and direct answer.Thanks
You’re welcome.
Unless this is a subpanel? Was there another disconnect before this one? I ask, because that 100 amp breaker is being backfed, and it also not secured to panel.
If that’s the case, it should not be bonded
