Dear Mario

All books was not writing the type lactate , I think you can use  any type (L or D)

It is non effect on bacteria growth 

please look sit web en.wikipedia.org/wiki/Sodium_lactate .

Dear Mario, it seems that there are 2 enzymatic systems for dehydrogenation of D L lactate. In addition many bacteria may have also lactate racemase that inter-converts these forms of lactate. Therefore, you might follow the advice of Niamah!

Thanks a lot for your answers! I've bought L-lactate!