Antilisterial activity of lactic acid bacteria isolated from rigouta, a traditional Tunisian cheese.
OBJECTIVE
Screening for lactic acid bacteria (LAB) producing bacteriocins and other antimicrobial compounds is of a great significance for the dairy industry to improve food safety.


RESULTS
Six-hundred strains of LAB isolated from 'rigouta', a Tunisian fermented cheese, were tested for antilisterial activity. Eight bacteriocinogenic strains were selected and analysed. Seven of these strains were identified as Lactococcus lactis and produced nisin Z as demonstrated by mass spectrometry analysis of the purified antibacterial compound. Polymerase chain reaction experiments using nisin gene-specific primers confirmed the presence of nisin operon. Plasmid profiles analysis suggests the presence of, at least, three different strains in this group. MMT05, the eighth strain of this antilisterial collection was identified, at molecular level, as Enterococcus faecalis. The purified bacteriocin produced by this strain showed a molecular mass of 10 201.33 +/- 0.85 Da. This new member of class III bacteriocins was termed enterocin MMT05.


CONCLUSIONS
Seven lactococcal strains producing nisin Z were selected and could be useful as bio-preservative starter cultures. Additional experiments are needed to evaluate the promising strain MMT05 as bio-preservative as Enterococci could exert detrimental or beneficial role in foods.


CONCLUSIONS
Only a few antibacterial strains isolated from traditional African dairy products were described. The new eight strains described herein contribute to the knowledge of this poorly studied environment and constitute promising strains for fermented food safety.
Ghrairi
T
T
Laboratoire de Biochimie et Biologie Moléculaire, Faculté des Sciences de Tunis, Campus universitaire, Tunis, Tunisia.
Manai
M
M
Berjeaud
J M
JM
Frère
J
J
D003086:Bacteriocin Plasmids / Q000235:genetics; D001430:Bacteriocins / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism; D002611:Cheese / Q000382:microbiology*; D003470:Culture Media; D013293:Enterococcus faecalis / Q000235:genetics / Q000302:isolation & purification; D005516:Food Microbiology; D013294:Lactococcus lactis / Q000235:genetics / Q000302:isolation & purification*; D008087:Listeria / Q000187:drug effects*; D008970:Molecular Weight; D009561:Nisin / Q000031:analogs & derivatives* / Q000032:analysis; D009876:Operon / Q000235:genetics; D014416:Tunisia
D001430:Bacteriocins; D003470:Culture Media; C495863:enterocin MMT05, Enterococcus faecalis; D009561:Nisin; C071364:nisin Z