Dear colleagues,
You are invited to the thesis viva of Frédérique DUFFES entitled:
Inhibition of Listeria monocytogenes by bactériocins from Carnobacterium
spp. in cold-smoked salmon. Preliminary work on resistance to divercin V41
by Two-dimensional electrophoresis.
The viva will take place :
the 08 october 1999 at 10h00,
in the lecture room of 3ème année INSFA
(65, rue de St Brieuc, 35042 Rennes, France)
Abstract :
Among 160 lactic acid bacteria, isolated from cold smoked salmon, vacuum
packed and stored at 8°C, 22 strains had been selected for their
bacteriocin activity against Listeria monocytogenes. Physiological,
biochemical and genetical characterisation evidenced that these strains
were Carnobacterium piscicola. Three different groups were determined by
pulsed field gel electrophoresis after DNA digestion, represented by C.
piscicola SF 668, C. piscicola SF 787 and C. piscicola SF 644.
Anti-Listeria activity has been tested firstly at 4°C in a simulated cold
smoked fish system and compared to C. divergens V41 and C. piscicola V1
activities, two strains isolated from trout viscera and whose bacteriocins
production, purification and mode of action had been well studied.
Carnobacterium piscicola SF 668 was the most active among the three new
strains. Its bacteriocins had been purified : C. piscicola SF 668 secreted
piscicocin V1A and a new bacteriocin of 1328 kDa with modified amino acids.
Listeria monocytogenes inhibition, on cold smoked salmon, vacuum packed and
stored at 4°C and 8°C, was significant for the three strains C. piscicola
SF 668, C. divergens V41 et. C. piscicola V1, with the highest efficiency
for this latter. No sensorial or biochemical significant spoilage has been
evidenced during all the storage period (three weeks), suggesting that
these strains could be use on the product. Purified bacteriocin (divercin
V41) or semi-purified (piscicocins V1 and nisin) had been tested in the
same conditions and showed a significant anti-Listeria activity. In this
case, it is the pure divercin V41 which had the highest inhibitory activity
at the two temperatures. No resistant variant has been isolated during this
study. Nevertheless, the mechanisms of resistance used by L. monocytogenes
had been studied, through protein profiles analysis by two-dimensional
electrophoresis of a sensitive and a resistant variants to the divercin
V41. Among 20 proteins produced by either of the two variants, two had been
identified as Listeria proteins. A ferritin and DNA-binding protein was
isolated from sensitive L. monocytogenes and flagellin from L.
monocytogenes resistant to divercin V41. The role of these two proteins in
resistance to bacteriocins is still unknown. This study show that some
strains of Carnobacterium, and their associated bacteriocins, are able to
preserve cold smoked salmon from L. monocytogenes development, without
spoilage of the product and without development of resistant cells. The
limits for bacteriocin industrial use are of technological and legislative
nature. This preliminary study on the mechanisms of resistance confirms
that it is a complex phenomenon as well as the molecular level, membrane
and cell wall levels and on the protein regulation pathways level.
Key words : Listeria monocytogenes, Carnobacterium spp., bacteriocins,
resistance, cold smoked.
Frédérique DUFFES
INRA/LRTL
65 rue de St Brieuc
35042 Rennes cedex
tel: 33/2/99/28/53/39
fax: 33/2/99/28/53/50
e-mail: duffes at labtechno.roazhon.inra.fr
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