212 Chapter 10
have occurred (Ahn et al. 1992 ; Tannock et
al. 1994 ; Lin et al. 1996 ; Gevers et al. 2003 ;
Ammor et al. 2008 )
Antimicrobial resistance in CNS has been
studied in detail due to its clinical relevance.
These bacteria display a high prevalence of
antibiotic resistance (Agvald - Ohman et al.
2004 ) and can constitute reservoirs of antibi-
otic - resistance genes that can be transferred
to other staphylococci (Wielders et al. 2001 ).
Antibiotic - resistant strains were found in
food (Gardini et al. 2003 ; Martin et al. 2006 ),
and genes for antimicrobial resistance to tet-
racycline, tet (M) and tet (K); erythromycin,
ermB and ermC ; and two β - lactams ( blaZ
and mecA) have been detected in CNS iso-
lated from fermented meat. Moreover, S.
xylosus strains, isolated from poultry infec-
tions, were found to be resistant to strepto-
gramins, harboring the vatB and the vgaB
genes.
An additional concern is that, even in the
absence of selective pressure, mobile genetic
elements carrying antibiotic resistance can be
transferred at high frequency through the
microbial community during sausage fer-
mentation (Vogel et al. 1992 ; Cocconcelli
et al. 2003 ).
For these reasons, the absence of acquired
resistance to an antibiotic of clinical rele-
vance should be a parameter to be used in the
selection of starter cultures for food.Toxigenic Potential
Some members of the CNS group, primarily
S. epidermidis , are common nosocomial
pathogens, and the presence of regulatory
elements, involved in the control of virulence
factor synthesis, has been recently identifi ed.
Remarkably, strains of S. xylosus were iso-
lated from patients who had an underlying
disease. The same species has been reported
to be involved in infections of poultry
(Aarestrup et al. 2000 ).
Although CNS of food origin has not been
found to produce nosocomial infections,history of apparent safe use, safety concerns
can be associated with lactic acid bacteria
and, more frequently, with CNS. A risk
factor potentially associated with all bacterial
groups used as starter cultures for sausage is
the presence of acquired genes for antimicro-
bial resistance.
The food chain has been recognized as
one of the main routes for the transmission
of antibiotic - resistant bacteria between
animal and human populations (Witte 2000 ).
The European Food Safety Authority has
recently concluded that bacteria deliberately
introduced in the food chains, such as the
starter cultures, might pose a risk to human
and animal health because of carrying
acquired resistance genes (EFSA 2007 ).
Fermented meats that are not heat treated
before consumption provide a vehicle for
such bacteria and can act as a direct link
between the indigenous microbiota of animals
and the human gastrointestinal tract.
Lactobacilli are generally recognized as
safe and are not responsible for human infec-
tions in healthy people (Z ’ Graggen et al.
2005 ). However, they might act as reservoirs
of transmissible antibiotic - resistance genes
that under certain conditions could be trans-
ferred to food or gut microbiota (Jacobsen
et al. 2007 ). In addition, the emergence of
antibiotic - resistant food - borne pathogens
originating from meat products (Doyle and
Erickson 2006 ) raises the question of the pos-
sibility of gene transfer between industrial
bacterial species and food - borne pathogens.
Several studies have reported antibiotic
resistance in LAB from meats and meat prod-
ucts; a few strains involved in sausage fer-
mentation such as L. sakei , L. curvatus , and
L. plantarum have been found to show such
resistance (Holley and Blaszyk 1997 ; Teuber
and Perreten 2000 ; Gevers et al. 2003 ). Some
genetic determinants, such as chlorampheni-
col acetyltransferase ( cat - TC), erythromycin
( erm B), and tetracycline ( tet L, tet M, and tet S
resistance genes), have been identifi ed, sug-
gesting that horizontal gene transfer may