Does adding turmeric to meat marinade negate the bacterial buildup at room temperature? I've learnt from this site that after applying marinade to meat, it has to be kept in the fridge for marination because meat at room temperature for more than two hours can have bacterial buildup, resulting in food poisoning.
In local meat shops in India, it's common for beef, chicken and fish vendors to leave raw meat at room temperature for most of the working day and yet do terriffic business. I havent had trouble with beef from such vendors but chicken and fish have caused food poisoning multiple times. Yet, no customer complains. These practices are too common.  

The question:
An elderly acquaintence (he is a building contractor; not a chef) was explaining how to marinate beef. Grind all the spices, mix salt, turmeric powder, corriander powder, mix well with the beef and leave it at room temperature for at least two hours.
When I interrupted to say I keep it in the fridge for marination, he said I should never do that since the flavours would not seep into the meat. Then I told him of the bacterial buildup and he promptly said: well, that's why we add turmeric powder for marination. Apparently the turmeric kills the bacteria.  

It sounded like hogwash to me, but I still wanted to ask here, since even I have felt that marination would work better if the meat is not too cold.
From the description in your question it looks like you're from India and Indian cuisine uses its native spices optimally and turmeric is proven to be antibacterial, however:


  How it works is still something of a mystery. The researchers know that curcumin tends to hang out within the bilayer more than in the vesicle’s central space. They suspect that when the sugar on the vesicle surface sticks to the cell wall of a passing bacterium, curcumin migrates into the cell and kills it from the inside.


Now onto the question what you should do: will the marinade be as tasty if you put it in the fridge?  Yes, of course, so both granny and you are correct:


Turmeric is antibacterial (though not a total disinfectant)
Putting the marinade straight into the fridge and leave it to marinade for 2 hours at 5°C will work nearly as well as leaving it out in 20-30°C from a pure taste perspective.


So use the best of both worlds: use granny's herb mix and refrigerate!

P.S. I leave my marinades for 2-24 hours in my fridge and I'm from a much cooler climate than you...
P.P.S. Don't freeze as -21°C will slow down the marination process too much and −273.15°C (absolute zero) will stop it completely!  ;-)