Is it safe to eat a cooked steak that (briefly) touched the plate that was holding the raw meat?
If you're at all like me, you are reassured by hard numbers and measurables. This should help.

In this situation one of the likely pathogens would be one of the Salmonella species. Salmonella is killed by temperatures in excess of 130 F (55 C). However, it's not an instant death. The time to kill Salmonella decreases exponentially as the temperature increases.

The following table represents all the temperature and duration to kill 99.9999% of the most heat-resistant strain Salmonella senftenberg. This species is as much as 30x more heat resistant than a "normal" S. typhimurium.


   Temperature | Time
---------------|------
 140 F (60 C)  | 60m
 150 F (65 C)  | 10m
 160 F (70 C)  | &lt;2m


For any given temperature the proportion of bacteria killed is constant. 1/6th the time kills 90%, 1/3rd kills 99%, 1/2 kills 99.9% etc.

USDA guidelines to kill Salmonella and E. Coli are as follows:


   Temperature | Time
---------------|------
 135 F (57 C)  | 86.4m
 140 F (60 C)  | 8.6m
 145 F (63 C)  | 2.7m
 150 F (65 C)  | 51.9s
 160 F (70 C)  | &lt; 6s
 165 F (74 C)  | &lt; 2s


So, needless to say, re-searing your steak at a typically high stove top temperature (at least 300 F [149 C]) for even a fraction of a second will result in utter devastation to whatever beastie population you may have picked up in recontaminating your meat. Chances are, if the steak came hot out of the pan, and you removed it from the plate quickly, the residual heat alone would be enough to kill it. The re-sear certainly doesn't hurt though.

A good rule of thumb is to wash plates as you go. If this is not possible or convenient you should minimally remove the plate from your vicinity by putting it in the sink or dishwasher as soon as you have taken the food off of it.