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Applied and Environmental Microbiology, September 2001, p. 4199-4205, Vol. 67, No. 9
Swiss Federal Dairy Research Station
Liebefeld, 3003 Bern, Switzerland
Received 24 April 2001/Accepted 27 June 2001
Raw milk was artificially contaminated with declumped cells of
Mycobacterium avium subsp. paratuberculosis at
a concentration of 104 to 105 CFU/ml and was
used to manufacture model hard (Swiss Emmentaler) and semihard (Swiss
Tisliter) cheese. Two different strains of M. avium subsp.
paratuberculosis were tested, and for each strain, two
model hard and semihard cheeses were produced. The survival of M. avium subsp. paratuberculosis cells was monitored
over a ripening period of 120 days by plating out homogenized cheese samples onto 7H10-PANTA agar. In both the hard and the semihard cheeses, counts decreased steadily but slowly during cheese ripening. Nevertheless, viable cells could still be detected in 120-day cheese.
D values were calculated at 27.8 days for hard and 45.5 days for semihard cheese. The most important factors responsible for
the death of M. avium subsp. paratuberculosis
in cheese were the temperatures applied during cheese manufacture and
the low pH at the early stages of cheese ripening. Since the ripening period for these raw milk cheeses lasts at least 90 to 120 days, the
D values found indicate that 103 to
104 cells of M. avium subsp.
paratuberculosis per g will be inactivated.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.9.4199-4205.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Fate of Mycobacterium avium subsp.
paratuberculosis in Swiss Hard and Semihard Cheese
Manufactured from Raw Milk
*
Corresponding author. Mailing address: Microbiology
Unit, Swiss Federal Dairy Research Station Liebefeld, Schwarzenburgstr. 161, CH-3003 Bern, Switzerland. Phone: 41 31 323-8192. Fax: 41 31 323-8227. E-mail: urs.spahr{at}fam.admin.ch.
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