Bacteriocins are natural metabolites produced by many strains of Lactic acid bacteria that used in food
preservation. They have potential healthy role in suppressing the growth of some spoilage and
pathogenic bacteria. The aim of the current study was to demonstrate the stability of the bacteriocin
extracted from Lactobacillus acidophilus at different pH values, heat treatments and proteinase K
enzyme. The obtained results revealed that the inhibitory effectiveness of bacteriocins was higher on
Gram-positive bacteria than Gram-negative bacteria. Further, the largest inhibition zone was obtained
by L. acidophilus bacteriocin against Bacillus subtilis while the smallest one was against E.coli. The
extracted bacteriocin exhibited broad spectrum of inhibition at concentration 6400AU/ml against Staph.
aureus, Bacillus subtilis and E.coli. The antimicrobial activity of crude supernatant fluid was stable
after heating at 100°C for 30 min and declined thereafter. Stability of antimicrobial activity was observed
at pH ranged from 2.0 to 8.0. Its active principle was proteinaceous in nature since the bacteriocin was
inactivated by proteinase K enzyme