Microbiological Aspects of Dairy Ingredients 81French cheeses have ranged from 0% to 23%,
with higher prevalence among unpasteurized
or raw milk cheeses (Little et al., 2008 ; De
Reu et al., 2002 ). Raw semi - hard and hard
cheeses had prevalence levels of 12.5% (De
Reu et al., 2002 ). No Staph. aureus was
detected in pasteurized retail semi - hard
cheeses (Little et al., 2008 ).
Staphylococcus aureus foodborne intoxi-
cation has been associated with the presence
of virulent staphylococcal enterotoxins,
which are heat - stable proteins produced by
approximately 25% of the Staph. aureus
strains isolated from food. Enterotoxin pro-
duction is generally associated with greater
than 5 log cfu/ml cell populations in milk.
Thus, cheeses made from raw milk under
EU regulations (D ’ Amico et al., 2008 ) must
contain fewer than 5 log cfu/ml at the time
of manufacture. If values greater than 5 log
cfu/ml are detected, the cheese must be tested
for enterotoxin presence.
Staphylococci are eliminated by pasteuri-
zation. However, enterotoxin produced in
milk can persist through cheese milk heat
treatments and lead to intoxication in the
fi nal product/ingredient. Staphylococcus
aureus is seldom found in cheeses made from
pasteurized milk or is found only in low
numbers (Little et al., 2008 ). Conversely,
Staph. aureus may increase 1.5 to 3 log units
in a wide variety of cheeses including
Camembert, feta, and semi - hard and hard
cheeses manufactured from raw milk under
normal conditions during cheese making.
This can be a 1 - to 1.5 - log unit increase
above normal curd entrapment concentration
of numbers. Larger increases in cell numbers
can result if starter culture activity is compro-
mised. Therefore, these cheeses are a poten-
tial health hazard, unless contamination of
milk is low and acidifi cation is optimal
(Zangerl and Ginzinger, 2001 ).
Studies have reported the stabilization of
Staph. aureus numbers during cheese making
when salt has been eliminated, apparently
due to inhibition of less salt – tolerant back-
ground microfl ora when salt is present (Ryser,by Schlesser et al. (2006) confi rmed that the
60 - day ripening period was inadequate to
eliminate E. coli 0157 : H7 during ripening of
cheddar cheese. Caro and Garcia - Armesto
(2007) reported the isolation of STEC from
Castellano cheese, a non - cooked hard or
semi hard variety prepared from ewe ’ s milk,
after a 12 - month ripening period. Using a
laboratory - scale smear ripened cheese pro-
duced from raw milk, Maher et al. (2001)
reported that E. coli 0157 : H7 was able to
grow during cheese manufacture and survive
during the ripening period up to 90 days.
Similarly, Leuschner and Boughtfl ower
(2002) and Arocha et al. (1992) showed that
E. coli 0157 could survive the soft cheese
manufacturing process. Escherichia coli
0157 : H7 also survived the manufacture and
storage of Camembert and feta cheeses at
2 ± 1 ° C for 65 and 75 days, respectively
(Raamsaran et al., 1998 ). Montet et al. (2009)
reported the growth of acid resistant and non -
acid - resistant shiga - toxin producing E. coli
during the early stages of Camembert manu-
facture and indicated that the 20 - day ripening
period for such cheeses may not guarantee a
safe product if STEC/VTEC is present in the
raw milk that is used.
Staphylococcus aureus. Dairy products,
including cheese, are known vehicles of
staphylococcal poisoning. Staphylococcus
aureus is commonly found in milk (D ’ Amico
et al., 2008 ; De Reu et al., 2002 ) and dairy
products made from either raw or pasteurized
milk (Coveney et al., 1994 ), because it is the
main etiological agent of bovine mastitis and
it is extensively carried by food industry
workers (Younis et al., 2003 ). Staphylococcus
aureus has been frequently associated with
foodborne outbreaks related to cheese made
from raw, unspecifi ed, or pasteurized milk in
the European Union (EU) (De Buyser et al.,
2003 ), although Ryser (2001) has indicated
the number of dairy - associated outbreaks in
the United States has decreased considerably
since the 1950s and 1960s.
Staphylococcus aureus has been detected
at varying levels in retail cheeses. Levels in