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Microbiological food safety of cheese produced in Swedish small-scale dairies

characteristics, growth and enterotoxin production of Staphylococcus aureus

Rosengren, Åsa (2012). Microbiological food safety of cheese produced in Swedish small-scale dairies. Uppsala : Sveriges lantbruksuniv.
ISBN 978-91-576-9074-6
[Licentiate thesis]

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Abstract

The number of small-scale dairies in Sweden has increased during the past decade. Current agricultural policy encourages such small-scale production and various ways to help producers have been proposed. Combining traditional cheese making and good product safety is a challenge, since several human pathogens pose a hazard in the products. Staphylococcus aureus is an important foodborne pathogen that can be transmitted via milk to cheese. Some strains can produce staphylococcal enterotoxin (SET) during growth in foods and cause food poisoning. Environmental conditions during the initial phase of cheese making are close to optimal for growth of S. aureus.

This study examined small-scale artisan cheese production and relevant pathogens, with the aim of formulating advice on microbiologically safe production. A survey of fresh and short-time ripened cheeses produced in Swedish small-scale dairies investigated the occurrence and levels of S. aureus, Listeria monocytogenes and Escherichia coli. Information about production practices was collected and S. aureus isolates were characterised with emphasis on enterotoxin genes, antibiotic resistance, biotyping and genetic variation. Staphylococcus aureus isolates from cheeses were investigated in broth cultures for their potential for growth and production of staphylococcal enterotoxin A (SEA) in typical cheese making conditions as regards temperature, pH, lactic acid/undissociated lactic acid and water activity.

Detected levels of the three pathogens were reasonable in most cheese samples tested. Listeria monocytogenes and SET were not found, but E. coli and enterotoxigenic S. aureus were frequently found in raw milk cheeses, sometimes at high levels. The S. aureus isolates were mainly of animal biotype and two-thirds were enterotoxigenic. The isolates tested were able to grow and produce SEA in the presence of moderate concentrations of undissociated lactic acid. SEA was produced continuously during incubation and high concentrations were found long after S. aureus levels had peaked. In practice, further storage of cheese samples prior to SET analysis may be beneficial when high staphylococcal levels are detected. Increased awareness of the importance of hygiene barriers is needed. Possible improvements in process control include e.g. controlling raw milk quality, using active starter cultures and monitoring acidification.

Authors/Creators:Rosengren, Åsa
Title:Microbiological food safety of cheese produced in Swedish small-scale dairies
Subtitle:characteristics, growth and enterotoxin production of Staphylococcus aureus
Year of publishing :2012
Number of Pages:60
Papers/manuscripts:
NumberReferences
I.Åsa Rosengren, Ane Fabricius, Bengt Guss, Susanne Sylvén and Roland Lindqvist (2010) Occurrence of foodborne pathogens and characterization of Staphylococcus aureus in cheese produced on farm-dairies. Int J Food Microbiol. 144 (2010) 263-269
II.Åsa Rosengren, Mats Lindblad and Roland Lindqvist. The effect of undissociated lactic acid on Staphylococcus aureus growth and enterotoxin A production. Submitted
Place of Publication:Uppsala
Publisher:Institutionen för mikrobiologi, Sveriges lantbruksuniversitet
ISBN for printed version:978-91-576-9074-6
Language:English
Publication Type:Licentiate thesis
Full Text Status:Public
Agris subject categories.:Q Food science > Q03 Food contamination and toxicology
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Microbiology (Microbiology in the medical area to be 30109)
(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Food Science
Agrovoc terms:cheese, staphylococcus aureus, enterotoxins, food safety, microbiological analysis, dairies, food hygiene, small enterprises, sweden
Keywords:Survey, Food safety, Cheese, Small-scale dairies, Lactic acid, Staphylococcus aureus, Growth rate, Lag time, Staphylococcal enterotoxin
URN:NBN:urn:nbn:se:slu:epsilon-e-471
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-471
ID Code:8811
Department:(NL, NJ) > Dept. of Microbiology (until 161231)
Deposited By: Unnamed user with email asa.rosengren@slv.se
Deposited On:04 May 2012 12:21
Metadata Last Modified:02 Dec 2014 10:50

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