Smearing of soft cheese with Enterococcus faecium WHE 81, a multi-bacteriocin
producer, against Listeria monocytogenes
Esther Izquierdo
a
, Eric Marchioni
a
, Dalal Aoude-Werner
b
, Claude Hasselmann
a
, Saı
¨
d Ennahar
a
,
*
a
Laboratoire de Chimie Analytique et Sciences de l’Aliment (UMR 7178), Faculte
´
de Pharmacie, IPHC-DSA, ULP, CNRS, 74 route du Rhin, 67400 Illkirch, France
b
Aerial, rue Laurent Fries, 67400 Illkirch, France
article info
Article history:
Received 8 April 2008
Received in revised form 31 July 2008
Accepted 3 August 2008
Available online 22 August 2008
Keywords:
Listeria monocytogenes
Enterococcus faecium
Enterocin
Cheese
abstract
Enterococcus faecium WHE 81, a multi-bacteriocin producer, was tested for its antimicrobial activity on
Listeria monocytogenes in Munster cheese, a red smear soft cheese. The naturally delayed and superficial
contamination of this type of cheese allowed the use of E. faecium WHE 81 at the beginning of the
ripening as a surface culture. A brine solution inoculated at 10
5
CFU of E. faecium WHE 81 per mL was
sprayed on the cheese surface during the first smearing operation. On day 7, smearing of cheese samples
with a brine solution at 10
2
CFU of L. monocytogenes per mL yielded initial cell counts of approximately
50 CFU g
À1
of the pathogen on the cheese surface. Although, in some instances, L. monocytogenes could
survive (<50 CFU g
À1
) in the presence of E. faecium WHE 81, it was unable to initiate growth. In control
samples however, L. monocytogenes counts often exceeded 10
4
CFU g
À1
. In other respects, E. faecium WHE
81, which naturally existed in Munster cheese, did not adversely impact on the ripening process.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
As a consequence of listeriosis outbreaks, with soft cheese being
the major food vehicle, today it is well established that this type of
cheese is amongst the products that pose the highest risk with
regard to human listeriosis (Rudolf and Scherer, 2001). Concern
over cheese-borne listeriosis has prompted research investigations
to examine the use of naturally occurring microflora, such as
bacteriocin-producing lactic acid bacteria, to reduce the incidence
of Listeria monocytogenes, the causative agent of listeriosis. Most
studies on soft cheese have used bacteriocin-producing bacteria as
starter cultures in milk and focused principally on white-mold
cheeses such as Camembert (Sulzer and Busse, 1991; Maisnier-Patin
et al., 1992; Wan et al., 1997). However, most probably due to
postprocess smearing operations, the incidence of L. monocytogenes
in red smear soft cheeses seems to be higher than in mold-ripened
cheeses (Lovett, 1988). In fact, smear cheeses are regularly washed
with a brine solution which represents a major means of contam-
ination and cross-contamination with L. monocytogenes (Bock-
elmann et al., 1997; Valde
`
s-Stauber et al., 1997; Carnio et al., 1999).
In addition, these cheeses provide excellent growth conditions
particularly on the surface where a rising pH-gradient develops
during ripening creating a more suitable environment for the
growth of L. monocytogenes (Terplan et al., 1986; Farber and
Peterkin, 1991; Ennahar et al., 1994).
Interestingly, the smearing operation can also be used as
a means of combating the pathogens by adding a bacteriocin
producer to the brine. This approach, which was developed in
a previous report on the use of the pediocin AcH producing
Lactobacillus plantarum WHE92 as a surface culture, proved to be
a viable strategy in helping to reduce cheese contamination with
Listeria (Ennahar et al., 1998b). These results, which were later
confirmed by Loessner et al. (2003), are mainly due to the fact that
L. monocytogenes is almost exclusively localized on the surface of
smear cheeses.
In recent years, enterococci were the focus of numerous inves-
tigations on bacteriocin production, mainly because bacteriocin
production seems to be a common trait among strains associated
with food systems (Franz et al., 2003). A large number of reports are
available on bacteriocin-producing enterococcal strains. Such
strains are in fact easily isolated from various foods and are most
likely to play a role in containing L. monocytogenes in food matrices,
especially since a vast majority of enterocins (enterococcal bacte-
riocins) are active against this pathogen of great concern to public
health (Giraffa, 2003; Hugas et al., 2003).
Enterococcus faecium WHE 81, isolated from Munster cheese
(Ennahar et al., 1998a), has been reported to be a putative multi-
bacteriocin producer with up to four independent antimicrobial
peptides produced, two of which are enterocins A and B (Ennahar
et al., 2001). Enterocins A and B, two pediocin-like bacteriocins
belonging to Class IIa bacteriocins are known to be effective
*
Corresponding author. Tel./fax: þ33 390 244 325.
E-mail address: ennahar@pharma.u-strasbg.fr (S. Ennahar).
Contents lists available at ScienceDirect
Food Microbiology
journal homepage: www.elsevier.com/locate/fm
0740-0020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.fm.2008.08.002
Food Microbiology 26 (2009) 16–20