Viability of Salmonella enterica subsp. enterica during the preparation and cold storage of Egyptian soft cheeses and ice-cream (original) (raw)
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Behavior of Yersinia enterocolitica and Salmonella typhimurium in Crottin goat's cheese
International Journal of Food Microbiology, 2005
In order to evaluate the behavior of Yersinia enterocolitica and Salmonella typhimurium in Crottin goat's cheese, inoculated products stored at 5, 15 and 25 8C were analysed together with chemical and microbiological characteristics of the cheese. In general, low counts of microorganisms were detected. None of the samples showed the presence of Escherichia coli, Salmonella spp. or Y. enterocolitica. In the inoculation tests, Y. enterocolitica and S. typhimurium were inhibited during storage; nevertheless, these bacteria survived for extensive periods. The counts at the end of the experiments at 5 and 15 8C were high, indicating that contamination with high bacterial numbers represents a potential health hazard. The primary mathematical models used to analyse the behavior of Y. enterocolitica and S. typhimurium were the Vitalistic, Gompertz's empirical and Churchill's model. The mean square error was calculated for the three models in order to evaluate the goodness-of-fit of each one. For Y. enterocolitica, the Vitalistic model was the best at the three temperatures. For S. typhimurium, there was no significant difference between the three models at 5 and 15 8C; the Churchill model was clearly the best at 25 8C. These results confirm that, in order to predict the risk of transmission of pathogenic microorganisms in foods using mathematical models, it is essential to analyse their behavior in specific foods.
Arab Univ. J. Agric. Sci., Ain Shams Univ., Cairo Special Issue, 26(2C), 1881 - 1894. , 2018
The study aims to assess the possibility of biological control on one of the most serious pathogenic microbes that found to infect Kariesh cheese, namely Salmonella typhimurium. To achieve this object, firstly a total of 20 Kariesh cheese samples were collected randomly from various markets located at Cairo and exposed to microbiological isolation and identification of S. typhimurium. The obtained results revealed that, S. typhimurium was detected in 30% of surveyed market Kariesh cheese according to the strain identified by polymerase chain reaction (PCR) technique. Secondary, five sewage water samples were obtained from Fac. of Agric., Ain Shams Univ., and Shoubra EL-Kheima station of drinking and sewage water for specific bacteriophage isolation and morphology particles of Salmonella bacteriophage was examined by transmission electron microscope. Third, pasteurized skimmed buffalo’s milk was converted into experimental Kariesh cheese at 40oC by milk inoculation with 2% of freshly activated yoghurt bacterial starter culture and then milk was divided into 5 equal portions. The 1st portion considered as control. The 2nd, 3rd, 4th and 5th portions were contaminated with equal level (1%) of S. typhimurium suspension containing 105 colony forming units (CFU)/mL, previously isolated from foregoing surveyed Kariesh cheese samples, followed by adding phage suspension, from which isolated from sewage water, containing 108 plaque forming units (PFU)/mL at the levels of nil, 1, 2 and 3% respectively. All portions were separately incubated at the same temperature up to curdling. The curds were cut and individually filled into stainless steel moulds lined with cheese cloth and consolidated by a slight pressure for 24 h. The blocks of curd were then cut, dry salted using 2% NaCl (w/w) and packaged into plastic containers. Experimentally, there were proportional reductions in lactic acid bacteria (LAB) population as the level of phage spiked into cheese milk increased, as which the reduction rate of LAB count during cold storage period (CSP) prolonging was however declined. In terms of health safety, although the number of pathogen microbe added was gradually reduced due to the acid developed by prolonging the Cold Storage Period in the absence of phage, but it stilled present until the end of experimental period. While, the pathogen was completely eliminated within 7 days of cheese age when the phage suspension (108 PFU/mL) has been spiked at the level of 1% at least. The contamination of experimental Kariesh cheese with S. typhimurium led to weaken the ability of cheese curd to drain whey as explained from the dry matter (DM) content which decreased due to the presence of pathogen and increased by the pathogen elimination with bacteriophage, which resulted also to increase the protein /DM content. The ash content reduced by both reasons, namely the contamination with S. typhimurium and/or the spiking level of phage suspension. The presence of S. typhimurium slowed the LAB population and acid production by them. Finally, as a conclusion, the spiking of Kariesh cheese milk with 1% Salmonella typhimurium phage suspension (108 PFU/mL) is quite enough to eliminate this microorganism when it present at the level of 1% suspension containing 105 CFU /mL.
Dairy Science & Technology, 2015
As cheese is often frozen prior to microbiological analysis, the aim of this study was to determine the survival of foodborne pathogens to freezing in cheese. A semi-soft cheese was produced, in independent triplicate for each pathogen mix, using milk inoculated with two pathogen mixes: Listeria monocytogenes+Staphylococcus aureus and Escherichia coli O157:H7+Salmonella typhimurium. Three different strains were used for each pathogen, except for E. coli O157:H7 for which two strains were used. Cheeses were manufactured, wrapped in plastic bags and frozen at −20°C. For the E. coli O157:H7+S. typhimurium pathogen mix, the effect of different freezing conditions on survival was studied. In all cases, the numbers of starter bacteria and pathogens were monitored in fresh cheese and after 2, 7, 30 and 90 days of storage. Two methods of thawing were compared after 30 days (14 h at 4°C and 4 h at 20°C). The numbers of L. monocytogenes, S. aureus and starter bacteria did not change significantly during frozen storage at −20°C, but E. coli and S. typhimurium decreased significantly after 2 days. There was no significant (p>0.05) influence of the thawing method. Freezing of cheese at −80°C or flash freezing in liquid nitrogen only facilitated survival of E. coli O157:H7 and S. typhimurium for 1 day. The study shows that cheese samples should not be frozen prior to analysis for detection or enumeration of E. coli or S. typhimurium.
Journal of Food Protection, 2014
Outbreaks of salmonellosis have been linked to the consumption of cheese, and emerging multidrug-resistant (MDR) strains of Salmonella may be more virulent and more tolerant than less resistant strains to stresses encountered in food production, which may enhance the survival of these resistant strains in cheese. This study was conducted to compare the behavior of MDR and pansusceptible Salmonella strains during the manufacture and aging of Gouda cheese and compare pathogen recovery via several rapid and traditional methods. Cheeses were manufactured from raw milk inoculated with a six-strain cocktail of either MDR or susceptible Salmonella Newport and Salmonella Typhimurium at initial levels of ~20 CFU/ml. Samples of milk, whey, curd, and finished cheese were analyzed using eight enrichment and detection protocols. Overall, changes in pathogen levels observed throughout manufacture and aging did not differ significantly between MDR and susceptible Salmonella strains. Salmonella cou...
Italian Journal of Animal Science, 2012
is a fresh pasta filata cheese produced from whole chilled buffalo milk. Although pasteurization of milk and the use of defined starter cultures are recommended, traditional technology involving the use of unpasteurized milk and natural whey cultures is still employed for WBMC production in Italy. The aim of this study were to assess the behaviour of Salmonella Typhimurium during the production of artisan water buffalo mozzarella cheese and during its shelf life under different temperature conditions. Raw milk was inoculated with S. Typhimurium and the evolution of S. Typhimurium count during production and shelf life was monitored. In artisan WBMC production technology S. Typhimurium multiplied in the curd during ripening, but its growth rate expressed in log CFU/g/h was lower than the growth rate reported by theoretical predictions. Stretching proved to be a process with good repeatability and able to reduce S. Typhimurium contamination by 5.5 Log CFU/g. The intrinsic characteristics of traditional WBMC proved to be unable to obstacolate the growth of S. Typhimurium during storage in the case of thermal abuse. Control of raw milk contamination and a proper refrigeration temperature are key factors in reducing the risk for consumers.
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.
Evaluation of a two-step protocol for rapid detection of Salmonella in ice-cream and Cheddar cheese
Food Microbiology, 2000
A two-step protocol for repair, multiplication and rapid detection of Salmonella species in ice-cream and Cheddar cheese was evaluated. The ¢rst step involves selective preenrichment using lactose broth supplemented with sodium pyruvate and yeast extract for the repair of injured cells and brilliant green for repression of the competing £ora (LBPYEBG). This enrichment is incubated for 7 h at 408C. The second step involves direct plating of 7 h selective preenrichment onto XLD agar and simultaneous inoculations into Salmonella 1^2 Test 1 for both isolation and presumptive identi¢cation of Salmonella the next day. The two-step protocol requires only 26+2 h for isolation and presumptive identi¢cation of Salmonella. This protocol was successfully used in detecting as few as 2 colony forming units (cfu) of non-stressed S. enteritidis per ml in 250 ml of enrichment. Initial inocula of 3 cfu ml 71 of freezethaw-injured S. enteritidis inoculated into various ice-creams grew to signi¢cantly (p 0?05) higher numbers after 6 and 7 h in the LBPYEBG enrichment than in the conventional lactose broth. This was also found to be true with a naturally contaminated ice-cream (MPN of 0?09 g 71 of S. enteritidis). S. typhimurium HF arti¢cially incorporated into Cheddar cheese grew more rapidly in the LBPYEBG enrichment than in the conventional lactose broth. This indicates the usefulness of this protocol for rapid detection of Salmonella spp. from ice-cream and Cheddar cheese.
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...
Journal of Advanced Veterinary and Animal Research, 2017
Objective: This study was conducted to determine the prevalence of Salmonella in milk (farm bulk milk, raw market milk) and cheese (kareish, white soft cheese) samples that were collected randomly from farms, supermarkets, small vendors and shops in different districts of Mansoura city, Egypt. Materials and methods: A total of 100 farm bulk milk, raw market milk, kareish cheese and white soft cheese samples (25 of each) were screened for the prevalence of Salmonella spp. The Salmonella isolates were isolated and identified by conventional bacteriological techniques, which were further confirmed genetically by polymerase chain reaction (PCR) based on the presence of invA gene. Finally, the isolates were serotyped. Results: Salmonella could be detected in 15%(n=15/100) samples with a prevalence of 12%(n=3/25), 24%(n=6/25), 20%(n=5/25) and 4%(n=1/25) in raw market milk, raw farm bulk milk, kareish cheese and white soft cheese, respectively. The Salmonella isolates were serotyped into S. enteritidis 33.3%(n=9/27) which was the most frequent, followed by S. typhimurium 25.9%(n=7/27), S. heidelberg 14.8%(n=4/27), S. infantis 11.11%(n=3/27), S. tsevie 11.11%(n=3/27) and S. haifa 3.7%(n=1/27). Conclusion: The present study confirms the presence of Salmonella in milk and cheese samples in Mansoura, Egypt, indicating that the dairy products can act as potential sources of Salmonella infection. Thus, appropriate hygienic measures are suggestive for combating Salmonellosis in Egypt.
Dairy, 2020
Survivability of Salmonella pathogens in commercial powdered goat milk (PGM) under different storage treatments was investigated using three batches of PGM products stored at two temperatures (4 °C and 25 °C) and ten storage periods (0, 3, 7, 14, 21, 30, 60, 90, 120 and 180 days). A cocktail of three Salmonella serotypes (Salmonella agona, Salmonella enteritidis and Salmonella tennessee) was inoculated to the PGM samples and then survival of Salmonella counts was enumerated in the inoculated and non-inoculated control groups. Results showed that the initial Salmonella counts were 7.103 Log CFU (colony forming unit)/g at both temperatures. At the first 3 days, the viable Salmonella counts were reduced about 0.94 and 1.40 Log CFU/g at 4 °C and 25 °C, respectively, where the same levels were sustained for 14 days. Further reductions continued and at the end of 180 days storage, Salmonella survivability was 1.15 Log CFU/g higher at 4 °C than at 25 °C under the same water activity condit...