Problem in acid tolerant test - (Jun/01/2014 )

Dear all, 

I have a question regarding the acid tolerant test on probiotic encapsulated cells. I have dissolved HPC into probiotic culture and spray dried to produce the final cfu as 39x10^10. Thus, I was tested this product towards acid tolerant test by incubated it with MRSB (pH3.5) for 90min. After incubation, I was performed serial dilution up to the power of 10. However, no colonies growth at all on the plate. May I know what is happening? Is it too diluted? Since the initial cfu is 39x10^10, is it meant that it has turn into 10^100 after I diluted it into serial dilution with the power of 10 again? 

Thank you. 

Run a control.