84 Chapter 3
shown to vary by cheese (Keogh, 1971 ). For
example, cheddar, Tilsit, and Bulgarian white
cheese contaminated with the tuberculous
agent were found to be infective after 220,
305, and 120 days, respectively, and
Camembert was found to be infective after 3
months (IDF 1980 ).
Mycobacterium avium subsp. paratuber-
culosis. The putative zoonotic potential of
Map has meant the survival of this bacterium
during cheese manufacture and ripening has
been investigated. Sung and Collins (2000)
determined a D value of 59.9 days for the
survival of Map in a soft Hispanic - style
cheese prepared under laboratory conditions;
Spahr and Schafroth (2001) calculated a D
value of 45.5 and 27.8 days for model hard
(Swiss Emmentaler) and semi - hard (Swiss
Tisliter) cheeses, respectively. The D values
estimated for the survival of three Map strains
during cheddar cheese manufacture were
107, 96, and 90 days (Donaghy et al., 2004 ).
Each of these cheeses have distinct character-
istics in terms of water content, starter cul-
tures, pH, and cooking temperatures, yet in
each case the inactivation of Map was slow
and gradual throughout the ripening period.
Map has been detected in retail cheeses in a
number of studies: 4.2% of raw milk Swiss
cheese samples by PCR (Stephan et al., 2007 )
and 5% of retail pasteurized cheese curds
(Wisconsin and Minnesota) by PCR (Clark
et al., 2006 ; Ikonomopoulos et al., 2005 ).
Many food safety agencies worldwide
have adopted the precautionary principle
toward Map, advocating the minimization of
entry into the food chain. Cheeses, especially
those derived from unpasteurized milk in
regions with a high prevalence of Johne ’ s
disease, will be scrutinized further should
evidence emerge to substantiate the zoonotic
nature of Map.Cheese Spoilage
Microbial spoilage of cheese is caused prin-
cipally by Gram - negative bacteria, Gram -
positive sporeformers, yeasts, and molds.highest risk with respect to Cl. botulinum.
Germination of spores present in such prod-
ucts can be prevented by proper cheese for-
mulation with regard to salt content, moisture
content, pH, nisin addition, and water activ-
ity. It is believed an onion - containing cheese
spread was responsible for an outbreak of Cl.
botulinum in Argentina (Briozzo et al., 1983 ),
which was due in part to toxin production in
a product having higher than normal water
activity. More recently, a canned cheese
sauce was traced to eight cases of botulinum
type A toxin. The cheese sauce formulation
supported Cl. botulinum growth and toxin
production which was exacerbated by tem-
perature abuse (Townes et al., 1996 ).
Mycobacterium bovis. Historically, the
consumption of unpasteurized milk, or prod-
ucts made from it, were the principal vehicles
of transmission of M. bovis to humans (de la
Rua - Domenech, 2006 ), a situation that
changed dramatically with the introduction
of pasteurization. Today in developed coun-
tries, one is more likely to fi nd tuberculosis
due to M. bovis in an aged person who
acquired the infection some 30 to 40 years
ago before the widespread adoption of pas-
teurization. However, there is an increasing
interest in artisan cheeses, some of which are
made from unpasteurized milk. A number of
recent cases of culture - positive tuberculosis
in the United States have been attributed to
M. bovis. Epidemiologic investigations indi-
cated the consumption of unpasteurized dairy
products, including soft fresh cheese origi-
nating from Mexico, may have accounted for
these cases. A follow - up survey for the pres-
ence of M. bovis in such products isolated M.
bovis from a panela - style cheese (n = 204)
(Harris et al., 2007 ; Kinde et al., 2007 ).
Jalava et al. (2007) suggest that exposure
to cattle or unpasteurized milk/dairy products
may be the most signifi cant risk factor for
human M. bovis disease. Because M. bovis
has been shown to be very resistant to chemi-
cal disinfectants, including acids and alkalis,
it is likely to survive for protracted periods
in cheese. However, this resistance has been