What do you mean by reactivate? Are you talking about the spore of lactobacilli? It should not be too difficult to activate them by put into medioum except they are extremely sensitive to antibiotics.

I meant to resuscitate the dormant cells. I have probiotic granules which showed 95% live cells using fluorescence spectrophotometer but no growth on agar plate. Thus, I was suspecting they have turns to become dormant cells and would like to resuscitate it. 

Hi Sherlyn

1-add 5 g of probiotic granules to 100 ml of skim milk and Incubate on 37 c for 24h 2-.Next day 5% of mother culture (stock culture) was add to 100ml skim milk and Incubate on 37 c for 24h. Repeat step second 3 times

Please inoculate into MRS broth and incubate for one week at 37 degree C. If u see little turbidity in the test tube then subculture it 3-4 times to get active culture from your dormant one. 

I agree with Nannu, Lactobacillus cells incubated in MRS broth and repeat 2-3 times and you also have your powerful strains.

as my previous answer

I think the best way and method for reactivate the lactobacilli is inoculation the bacterium in MRS broth and following that incubation in incubator in appropriate temperature for lactobacilli (30 or 37C) in anaerobic condition like gas pack in a jar and after appearing the colony on agar plate or after appearing the turbidity in MRS broth, then you can reinoculate in another MRS medium and repeat this method 3 or 4 times, also you can use Skim milk for reactivation of this genus (lactobacilli)

If bacterium did not reactivate according to above methods, please inoculate bacterium (100-300 microlitres) into 10 ml MRS broth containing yeast extract and BHI, and incubated at 37C for 3-4 days under anaerobic conditions. After appearing the turbidity in MRS broth containing yeast extract , please repeat this method in MRS broth containing yeast extract  for 3 times. But, if you did not see any growth in MRS broth containing yeast extract , please inoculate bacterium from BHI into MRS broth containing yeast extract (1-3%) once. Then, repeat this method in MRS broth containing yeast extract.

Good luck