Background: A total of 94 lactic acid bacteria (LAB)
were isolated from Tunisian artisanal (Ricotta cheese’s whey) and
industrial (bactofugate) milk waste, identified and then screened for
their antimicrobial activity against some bacteria implicated on
Objective: Bacterial genera and species identification was performed
using molecular tools. The antimicrobial activity was tested against
7 strains of Gram-negative bacteria and 4 strains of Gram-positive
bacteria as well as 6 yeasts.
Method: The Crude extract was found to have a narrow antimicrobial spectrum on
Gram-positive bacteria mainly Listeria monocytogenes. Among the strains which
showed antibacterial activity, four were determined to be bacteriocins-producers.
They were identified as Lactococcus lactis.
Results: Brain Heart Infusion (BHI) Agar was found more adapted than Man, Rogosa
and Sharpe (MRS) to investigate the antimicrobial activity of L. actococcus lactis
against L. isteria monocytogenes. The genetic determinants encoding the antimicrobial
peptides were targeted by specific PCR.
Conclusion: All L. lactis bacteriocin producing strains possessed the Nisine Z gene
(nisZ) except for one, which contained both Nisine A and Nisine Z genes (nisA and
nisZ). They have been identified as antilisterial agentS.