Microbiological Aspects of Dairy Ingredients 83Blanco cheese was responsible for an out-
break among mainly Hispanic patients in the
United States during the 1980s. Brucella spp.
have been isolated from 7.5% of Mexican
cheese samples (Acedo et al., 1997 ) and 5%
of retail soft Mexican cheeses (Ongor et al.,
2006 ). In the latter study, all detected strains
(by PCR) were identifi ed as Br. abortus. This
species and Br. melitensis have been detected
in raw sheep ’ s milk cheeses in Turkey
(Sancak et al., 1993 ) and in 2.2% of French
cheeses manufactured in Iran (Akbarmehr,
2003 ). The consumption of unpasteurized
cheese has been identifi ed as a key risk factor
for brucellosis in Iran, which is also appli-
cable to raw milk cheeses produced in regions
where brucellosis is endemic. Challenge
studies performed with Camembert, Tilsit,
and cheddar indicate the survival of Br.
abortus up to 57, 15, and 180 days post man-
ufacture, respectively. However, pasteuriza-
tion provides adequate margins of safety for
Brucella spp. in milk.
Clostridium botulinum. Clostridium bot-
ulinum outbreaks associated with dairy prod-
ucts are rare and sporadic. Since 1980, three
cheese - borne outbreaks have been reported,
each resulting from toxin A type poisoning.
One fatality resulted from each of the out-
breaks, the largest of which was in Iran and
involved 27 cases (Pourshafi e et al., 1998 ). A
traditional Iranian cheese preserved in oil
was the incriminating food source. A com-
mercial Mascarpone cheese was the cause of
a Cl. botulinum outbreak in Italy in 1996. The
cheese had been eaten by all of the patients,
either alone or as the uncooked ingredient of
the dessert tiramisu. Clostridium botulinum
type A and the associated toxin were detected
in tiramisu leftovers and retail samples of the
Mascarpone cheese. It is believed that a
break in the cold chain at retail likely caused
germination of Cl. botulinum spores with
subsequent production of the toxin (Aureli
et al., 2000a ).
Anaerobically packaged cheese products,
for example, cheese spreads, may present thelinked milk outbreaks, is not uncommon.
This can be due to:
- A low level of contamination of the impli-
cated product - The fact that Campylobacter spp. initially
present in milk do not proliferate and
usually die within a few days - The use of insensitive detection methods
Although Camp. jejuni DNA has been
detected in cheese samples (Wegmuller,
1993 ) by PCR and unconfi rmed by culture,
the cheese challenge studies to date and the
fastidious nature of campylobacters support
the assertion that cheese is an unlikely vehicle
of transmission for Campylobacter enteritis.
In the limited number of surveys of cheese
products for campylobacters, none have
recovered the organism from French raw
milk cheese (Federighi et al., 1999 ), cheddar
(Brodsky, 1984a ), or Canadian - produced
Brie and Camembert (Medeiros et al., 2008 ).
Campylobacter spp. are unable to grow at
refrigeration temperatures and low pH, and
are readily inactivated at cooking tempera-
tures encountered in cheeses such as cottage
cheese or Swiss hard and semi - hard cheeses
(Bachman and Sphar, 1995 ).
Brucella spp. Although major outbreaks
of brucellosis with cheese identifi ed as the
food vehicle of transmission are rare, there
have been outbreaks linked to Mexican
Queso Fresco cheese and sheep/goat ’ s milk
soft cheese (Table 3.3 ). The latter outbreaks
have been caused by Br. melitensis and have
generally resulted from the consumption of
unpasteurized cheese manufactured in a
country with endemic brucellosis. For
example, cheese - borne brucellosis in England
and Wales (1981 to 1983) was associated
with sheep and goat cheese imported from
Italy and Jordan. Other cases occurring in
England and Wales were linked with a major
outbreak in Malta (1995), in which unpas-
teurized sheep and goat ’ s milk was identifi ed
as the vehicle of infection. Contaminated raw
goat ’ s milk used to manufacture Queso