Loss of viability of Listeria monocytogenes in contaminated processed cheese during storage at 4, 12 and 22°C (original) (raw)
Related papers
Survival of Listeria monocytogenes in Cold-Pack Cheese Food During Refrigerated Storage
Journal of Food Protection, 1988
Duplicate lots of cold-pack cheese food were manufactured, according to nine different formulations, inoculated to contain ca. 5 x 102 Listeria monocytogenes (strains Scott A, V7, California or Ohio) colony forming units (CFU)/g and stored at 4°C. L. monocytogenes in cheese food was enumerated by surface-plating appropriate dilutions made in tryptose broth containing 2% (w/v) sodium citrate (TBC) on McBride Listeria Agar (MLA). Initial TBC dilutions were stored at 3°C and surface-plated on MLA after 2, 4, 6 and 8 weeks if the organism was not quantitated by direct plating of the original samples. Selected Listeria colonies were confirmed biochemically. Populations of L. monocytogenes in cheese food manufactured without preservatives or acidifying agents generally decreased less than 10-fold after 182 d of storage. However, numbers of L. monocytogenes steadily decreased in cheese food containing 0.30% sorbic acid or 0.30% sodium propionate and which was acidified to pH 5.0 to 5.1 with lactic and/or acetic acid. In cheese food preserved with 0.30% sorbic acid, L. monocytogenes survived an average of 130 d in non-acidified cheese food and 112, 93 or 74 d in cheese food acidified with lactic acid, lactic plus acetic acid, or acetic acid, respectively. When 0.30% sodium propionate was substituted for sorbic acid, L. monocytogenes survived an average of 142 d in non-acidified cheese food and 118, 103 or 98 d in cheese food acidified with lactic, acetic, or lactic plus acetic acid, respectively. Since 1983, at least 150 cases of listeriosis, including 54 deaths, resulted from consumption of pasteurized milk (17) and Mexican-style cheese (20) contaminated with Listeria monocytogenes. Recently, another outbreak reported in Switzerland resulted from consumption of Vacherin Mont d'Or soft-ripened cheese (13) and caused at least 10 cases of listeriosis, including two deaths. Increased surveillance of the dairy industry by the Food and Drug Administration, prompted by outbreaks of listeriosis associated with dairy products, has lead to isolation of L. monocytogenes from a variety of domestic cheeses including Liederkranz (2,3), Mexican-style (1,7), Ricotta (22) and Cheddar (22), as well as Brie (4,5,6,9), semi-soft (8) and soft-ripened cheese (8) imported from France. When these findings are considered along with numerous isolations of L. monocytogenes from the dairy factory environment, clearly, this organism poses a serious threat to the cheese industry. Cold-pack cheese food is defined by regulation with a Standard of Identity; Title 21, part 133.124. (18). Several dairy ingredients used in the manufacture of cold-pack cheese food, i.e. Cheddar cheese, nonfat dry milk, and dried whey, could serve as vehicles for contamination of the finished product with L. monocytogenes. Currently, Cheddar cheese manufactured from raw milk can be used in cold-pack cheese food if the cheese is ripened at > 35 °F (1.7°C) for > 60 d to eliminate pathogenic organisms (18). However, experimental evidence has shown that L. monocytogenes can survive as long as 434 d in Cheddar cheese ripened under these conditions (25). In addition, a recall because of contamination with L. monocytogenes was recently issued for raw milk Cheddar cheese which was properly ripened (22). Another study (75) showed that L. monocytogenes can survive as long as 84 d in nonfat dry milk manufactured from pasteurized skim milk inoculated to contain ca. 105 colony forming units (CFU)/ml. Ryser and Marth (26) demonstrated that L. monocytogenes can grow to levels of ca. 108 CFU/ml in filter-sterilized whey. Based on these results, the pathogen would likely survive during spray-drying of fluid whey. Recently, salted (1.2 and 2.5% NaCl) and unsalted butter were manufactured from pasteurized cream inoculated to contain ca. 104 to 105 L. monocytogenes strain Scott A CFU/g (28). After 70 d of storage at-18, 4 and 13°C, the organism was present at levels of 3.22, 5.26 and 5.84 logio CFU/g of butter, respectively. Although L. monocytogenes has yet to be isolated from commercially produced cold-pack cheese food, ingredients used to manufacture this product are clearly capable of harboring the bacterium. The presence of L. monocytogenes in coldpack cheese food is of special concern since this product receives no further heat treatment or aging and is normally consumed shortly after manufacture. Recent recalls of Lwfen'a-contaminated cheeses have
2011
The objective of the present study was to determine the effect of L. monocytogenes physiology and the stage of contamination on its behaviour during production and ripening of Kefalograviera and Feta cheese. L. monocytogenes inocula of different physiological states were evaluated for their survival in Kefalograviera and Feta cheese stored at 4 o C. Specifically, planktonically grown and detached L. monocytogenes cells were prepared as inocula, when a multi-strains composite of L. monocytogenes isolates was left to grow in TSBYE with 1% glucose (acid adapted) or without glucose (nonadapted), MRD, milk, Feta and Graviera cheese in the presence of stainless steel coupons (2x5cm 2 ) for 4 d at 20°C and then detached by bead vortexing. In Graviera cheese, L. monocytogenes cells survived throughout storage (82 days) at low concentration (<2 log CFU/ml). At Feta cheese the total of inocula were below the detection limit by the 18th day of storage. In both cheeses TSBYE biofilms and mil...
International Journal of Food Microbiology, 2011
The dynamics of the physicochemical characteristics of foods help to determine the fate of pathogens throughout processing. The aim of this study was to assess the behaviour of Listeria monocytogenes during cheesesmaking and ripening and to model the growth observed under the dynamic conditions of the cheese. A laboratory scale cheese was made in 4 independent replicates from pasteurised or raw cow's milk, artificially contaminated with L. monocytogenes. No growth of L. monocytogenes occurred during raw milk cheese-making, whereas growth did occur in pasteurised milk. During ripening, growth occurred in raw milk cheese, but inactivation occurred in pasteurised milk cheese. The behaviour observed for L. monocytogenes was modelled using a logistic primary model coupled with a secondary cardinal model, taking into account the effect of physicochemical conditions (temperature, pH, water activity and lactate). A novel statistical approach was proposed to assess the optimal growth rate of a microorganism from experiments performed in dynamic conditions. This complex model had an acceptable quality of fit on the experimental data. The estimated optimum growth rates can be used to predict the fate of L. monocytogenes during cheese manufacture in raw or pasteurized milk in different physicochemical conditions. The data obtained contributes to a better understanding of the potential risk that L. monocytogenes presents to cheese producers (growth on the product, if it is contaminated) and consumers (the presence of high numbers) and constitutes a very useful set of data for the completion of chain-based modelling studies.
International Journal of Dairy Technology, 2016
This study investigated the behaviour and fate of Listeria monocytogenes at different ripening temperatures and NaCl concentrations in traditional Lighvan cheese. L. monocytogenes was added to raw sheep's milk. After producing the cheese, they were stored in 8%, 12% and 15% NaCl at 4, 9 and 14°C. Sampling was performed for 150 days. Different temperature and NaCl concentrations had a significant effect on the survival of L. monocytogenes (P < 0.001). The lowest growth and survival rates of L. monocytogenes were in 15% NaCl at 14°C and 12% NaCl at 14°C, respectively. Also, the highest growth and survival rates of the bacterium were in 8% NaCl at 4°C.
International Journal of Food Microbiology, 2017
As reported on RASFF's portal, in the first 9 months of 2016, a total of 13 "alerts/information for attention" were issued concerning the presence of Listeria monocytogenes in mould cheeses throughout Europe. This study analyzes the behaviour of L. monocytogenes in Gorgonzola cheese, a typical Italian soft blue-veined cheese, when contaminated at different time points. In the first challenge test, the pasteurized milk was contaminated and the complete cheese manufacture (cheesemaking, ripening) and shelf life was simulated. After a decrease during the first days of the cheesemaking, the pH remained constant for 35 days (5 weeks) and then it increased rapidly reaching the final values of 6.8 ± 0.02 in the core and 5.8 ± 0.4 on the rind. At the same time, the pathogen concentration decreased (about 2 log CFU/g), although during the last week a rapid pathogen growth was observed after the rise in pH values. When the cheese was stored at thermal abuse condition (8-12°C), the pathogen concentration on the rind was 4.8 ± 0.3 log CFU/g and after 66 days (about 9 weeks) no significant difference (p > 0.05) was observed; whereas, a growth from 5.4 ± 0.4 to 7.1 ± 0.5 log CFU/g was observed in the core. A second challenge test was performed using three batches of commercial slices of Gorgonzola cheese inoculated by L. monocytogenes and stored at 8°C. The maximum specific growth rates (μ max , 1/h) of L. monocytogenes estimated ranged from 0.007 to 0.061. The square root model was used to predict the μ max at others temperature and to establish the time necessary to reach the European critical legal limit of 2 log CFU/g, in different storage scenarios. The predictions obtained in this study can be applied to any time-temperature profile, and in particular to the conditions to which the product is most likely to be subject in normal use, up to its final consumption. This study can be considered a valuable contribution also aimed at supporting the monitoring surveys carried out by officers of the Regional Veterinary Authority.
2014
A potentially hazardous food (PHF) requires time/temperature control to maintain safety. The US Food and Drug Administration would classify most cheeses as PHF based on pH and a w, and a product assessment would be required to evaluate safety for >6 h storage at 21°C. We tested the ability of 67 market cheeses to support growth of Listeria monocytogenes (LM), Salmonella spp. (SALM), Escherichia coli O157:H7 (EC), and Staphylococcus aureus (SA) over 15-day storage at 25°C. Hard (Asiago and Cheddar), semi-hard (Colby and Havarti), and soft cheeses (Mozzarella and Mexican-style) were among types tested, and included some reducedsodium and reduced-fat types. Single-pathogen cocktails were prepared and individually inoculated onto cheese slices (~10 5 CFU/g). Cocktails were comprised of 10 strains of LM, six of SALM, or five of EC or SA. Inoculated slices were vacuum packaged and stored at 25˚C for < 15 days, with surviving inocula enumerated every three days. Salt-in-the-moisture phase (%SMP), calculated from measured moisture (%) and salt (%), titratable acidity (%), pH, and a w were measured. Pathogens did not grow on 53 cheeses, while 14 cheeses supported growth of SA, six of SALM, four of LM, and three of EC. Of the cheeses supporting pathogen growth, all supported growth of SA, ranging from 0.57 to 3.08 log CFU/g (avg. 1.70 log CFU/g). Growth of SALM, LM, and EC ranged from 1.01 to 2.05 log CFU/g (avg. 2.05 log CFU/g), 0.60 to 2.68 log CFU/g (avg. 1.60 CFU/g), and 0.41 to 2.90 log CFU/g (avg. 1.69 CFU/g), respectively. Cheese pH and %SMP most affected pathogen growth, with pH having a dominant effect. Pathogen growth/no-growth varied within some cheese types or lots. Except for Swiss-type cheeses, moldor bacterial-ripened cheeses, and cheeses made with non-bovine milk where insufficient data exists, the pathogen growth/no-growth interface could be modeled and boundary conditions established for safe, extended storage (<25°C) of cheeses based on pH and %SMP.
International Journal of Food Microbiology, 2014
Nuts and seeds have been increasingly associated with recalls due to contamination with Listeria monocytogenes. Storage of these food commodities occurs at various relative humidity (RH) conditions for months or years. The objective of this study was to assess L. monocytogenes survival on four commodities representing dried legumes, seeds, and spices categories: chickpeas, sesame seeds, pine nuts, and black pepper kernels. Inoculated products at 10 log CFU/g were stored for 180 days (6 months) at 25˚C and different relative humidity (RH) levels: 25% (low), 45% (ambient), and 75% (high). After 180 days at 25% RH, L. monocytogenes populations decreased to 2.67-6.59 log CFU/g; the highest survival of the pathogen was observed on pine nuts and sesame seeds with decay rates of-0.014± 0.001 log CFU/g per d. Significantly greater population reductions on all products were observed during storage at 45 and 75% RH. At 45% RH, L. monocytogenes levels decreased to 1.90-6.36 log CFU/g. On chickpeas and black pepper stored at 75% RH, the pathogen population decreased to below the limit of enumeration (1 log CFU/g) yet were still detected via enrichments. The lowest survival of L. monocytogenes occurred at 75% RH on black pepper with a decay rate of-0.058±0.003 log CFU/g per d. Overall, regardless of RH level, the ability of the products to support survival of the pathogen may be expressed in the following order: pine nuts > sesame seeds > chickpeas > black pepper. The results of this study can aid in understanding how L. monocytogenes survives on dried legumes, seeds, and spices, and the data can contribute to the risk assessment of this pathogen.
Journal of food protection, 2014
Potentially hazardous foods require time/temperature control for safety. According to the U.S. Food and Drug Administration Food Code, most cheeses are potentially hazardous foods based on pH and water activity, and a product assessment is required to evaluate safety of storage >6 h at 21°C. We tested the ability of 67 market cheeses to support growth of Listeria monocytogenes (LM), Salmonella spp. (SALM), Escherichia coli O157:H7 (EC), and Staphylococcus aureus (SA) over 15 days at 25°C. Hard (Asiago and Cheddar), semi-hard (Colby and Havarti), and soft cheeses (mozzarella and Mexican-style), and reduced-sodium or reduced-fat types were tested. Single-pathogen cocktails were prepared and individually inoculated onto cheese slices (∼10(5) CFU/g). Cocktails were 10 strains of L. monocytogenes, 6 of Salmonella spp., or 5 of E. coli O157:H7 or S. aureus. Inoculated slices were vacuum packaged and stored at 25°C for ≤ 15 days, with surviving inocula enumerated every 3 days. Percent s...
Survival of Listeria monocytogenes During Manufacture and Storage of Cottage Cheese
Journal of Food Protection, 1985
Cottage cheese was made by the short-set procedure in pilotplant-sized vats from pasteurized skim milk inoculated to contain 10 4-10 5 Listeria monocytogenes (strains Scott A or V7)/ ml. Half the curd from each trial (two trials with each strain of L. monocytogenes) was creamed and half remained uncreamed. Numbers of L. monocytogenes were determined by surface-plating samples diluted in Tryptose Broth (TB) on McBride's Listeria Agar (MLA). Initial TB dilutions were then stored at 3°C and plated on MLA after 2, 4, 6 and 8 weeks or until L. monocytogenes was recovered. Selected L. monocytogenes colonies from each sample were serologically confirmed. Results for both strains indicate that during manufacture, numbers of L. monocytogenes remained relatively constant until after cooking of curd was completed. All samples analyzed after cooking curd 30 min at 57.2°C (135°F) contained fewer viable L. monocytogenes than could be detected by our methods (10 or 100 CFU/g or ml). Both strains were recovered from cold-enrichment samples, indicating that small numbers of the organism survived the cheesemaking process. Using direct plating onto MLA, L. monocytogenes was recovered from 43 of 112 (38.4%) cottage cheese samples during storage at 3°C for up to 28 d. After cold-enrichment in TB for up to 8 weeks, 59 of 112 (52.7%) samples were positive forL. monocytogenes. Greater numbers of L. monocytogenes, particularly strain Scott A, were found in creamed rather than uncreamed cottage cheese; however, numbers seldom exceeded 100/g. Listeria monocytogenes is a potential foodborne pathogen which can cause abortions in pregnant women and meningitis or meningio-encephalitis in immunocompromised men and women (6,13,14). In dairy cattle, L. monocytogenes can cause mastitis and abortion, leading to excretion of the organism in milk from the infected animal (4,5,15). Evidence for the role of milk in transmission of L. monocytogenes from infected dairy cattle to man has appeared in European literature. The first reported massive outbreak of human listeriosis occurred in Halle, Germany and was followed by epidemics in Jena, Germany and Prague, Czechoslovakia (14). Consumption of Listeriacontaminated raw milk was believed to be the cause of human illness.
The survival of Listeria monocytogenes in cottage cheese
The Journal of applied bacteriology, 1991
Because of the difficulty of ensuring that cottage cheese is produced in conditions that prevent contamination with Listeria monocytogenes, the ability of this bacterium to survive in cottage cheese from three sources was investigated (a) during shelf-life at chill temperature and (b) in conditions of temperature abuse. Three batches of creamed cottage cheese, from three sources, received within 24 h of production, were inoculated with L. monocytogenes strain F6861 and stored at 4, 8 or 12 degrees C for 14 d. The three batches differed in their initial pH, titratable acidity and content of lactic acid and of lactic acid bacteria. No increase in numbers of L. monocytogenes occurred in the cottage cheeses during storage in these conditions. The numbers of listeria decreased; the rate of decrease differed in products from the three sources and was least in the product with the highest pH and lowest content of lactic acid. Acid formation by lactic acid bacteria during storage of the pro...