Survival of Listeria monocytogenes in Vanilla-Flavored Soy and Dairy Products Stored at 8°C

2004 ◽  
Vol 67 (2) ◽  
pp. 378-382 ◽  
Author(s):  
SIREESHA TIPPARAJU ◽  
SADHANA RAVISHANKAR ◽  
PETER J. SLADE
Keyword(s):  
Listeria Monocytogenes ◽  
Dairy Products ◽  
Storage Time ◽  
Viable Cell ◽  
Inhibitory Effect ◽  
Soy Milk ◽  
Low Fat ◽  
Log Reduction ◽  
Milk Samples ◽  
Cell Counts

The survival of Listeria monocytogenes V37 in vanilla-flavored yogurt (low-fat and nonfat) and soy milk (low-fat and Plus) stored at 8°C for 31 days was investigated. Commercial samples of yogurt and soy milk were used. These samples were inoculated with either 104 or 107 CFU of L. monocytogenes per ml. Sampling was carried out every 3 to 4 days initially and was then carried out weekly, for a total storage time of 31 days. Each time a sample was collected, the pH of the sample was measured. After 31 days, low-fat plain, low-fat vanilla, and nonfat plain yogurt samples inoculated with 104 CFU/ml showed 2.5-log reductions in viable cell populations, and nonfat vanilla yogurt showed a 3.5-log reduction. For yogurt inoculated with 107 CFU/ml, reductions of 2.5 log CFU/ml were observed for plain low-fat and nonfat yogurts, and reductions of 5 log CFU/ml were observed for vanilla-flavored low-fat and nonfat yogurts. In vanilla-flavored and plain low-fat and Plus soy milk samples, cell counts increased from 104 and 107 CFU/ml to 109 CFU/ml at 7 and 3 days of storage, respectively, at 8°C. Coagulation in soy milk samples was observed when the cell population reached 109 CFU/ml. In soy milk, the L. monocytogenes population did not change for up to 31 days. Vanillin had an inhibitory effect on L. monocytogenes in yogurt but not in soy milk.

scholarly journals Viable and Total Bacterial Populations Undergo Equipment- and Time-Dependent Shifts during Milk Processing

2019 ◽  
Vol 85 (13) ◽  
Author(s):  
Mary E. Kable ◽  
Yanin Srisengfa ◽  
Zhengyao Xue ◽  
Laurynne C. Coates ◽  
Maria L. Marco
Keyword(s):  
Dairy Products ◽  
Dairy Product ◽  
Marker Gene ◽  
Late Summer ◽  
Viable Cell ◽  
Bacterial Composition ◽  
Cell Numbers ◽  
Milk Samples ◽  
Viable Cells ◽  
High Temperature Short Time

ABSTRACT We set out to identify the viable and total bacterial content in milk as it passes through a large-scale, dairy product manufacturing plant for pasteurization, concentration, separation, blending, and storage prior to cheese manufacture. A total of 142 milk samples were collected from up to 10 pieces of equipment for a period spanning 21 h on two collection dates in the spring and late summer of 2014. Bacterial composition in the milk was determined by 16S rRNA marker gene, high-throughput DNA sequencing. Milk samples from the late summer were paired such that half were treated with propidium monoazide (PMA) to enrich for viable cells prior to quantification by PCR and identification by DNA sequence analysis. Streptococcus had the highest median relative abundance across all sampling sites within the facility on both sampling dates. The proportions of Anoxybacillus, Thermus, Lactococcus, Lactobacillus, Micrococcaceae, and Pseudomonas were also elevated in some samples. Viable cells detected by PMA treatment showed that Turicibacter was enriched after high-temperature short-time pasteurization, whereas proportions of Staphylococcus were significantly reduced. Using clean-in-place (CIP) times as a reference point, Bacillus, Pseudomonas, and Anoxybacillus were found in high relative proportions in several recently cleaned silos (<19 h since CIP). At later times (>19 h after CIP), 10 of 11 silos containing elevated viable cell numbers were enriched in Acinetobacter and/or Lactococcus. These results show the tremendous point-to-point and sample-dependent variations in bacterial composition in milk during processing. IMPORTANCE Milk undergoes sustained contact with the built environment during processing into finished dairy products. This contact has the potential to influence the introduction, viability, and growth of microorganisms within the milk. Currently, the population dynamics of bacteria in milk undergoing processing are not well understood. Therefore, we measured for total and viable bacterial composition and cell numbers in milk over time and at different processing points in a cheese manufacturing facility in California. Our results provide new perspectives on the dramatic variations in microbial populations in milk during processing even over short amounts of time. Although some of the changes in the milk microbiota were predictable (e.g., reduced viable cell numbers after pasteurization), other findings could not be easily foreseen based on knowledge of bacteria contained in raw milk or when the equipment was last cleaned. This information is important for predicting and controlling microbial spoilage contaminants in dairy products.

Identification and Enumeration of Beta-Hemolytic Listeria monocytogenes in Naturally Contaminated Dairy Products

1988 ◽  
Vol 71 (3) ◽  
pp. 673-675
Author(s):  
Atin R Datta ◽  
Barry A Wentz ◽  
Walter E Hill
Keyword(s):  
Listeria Monocytogenes ◽  
Dairy Products ◽  
Dna Probe ◽  
Milk Samples ◽  
Unpasteurized Milk ◽  
Pure Cultures ◽  
Camp Test

Abstract A DNA probe was used to identify hemolytic Listeria monocytogenes in naturally contaminated dairy products: unpasteurized milk, ricotta cheese, and imported semisoft cheeses. Of 34 milk samples, 12 were suspected to contain hemolytic L. monocytogenes; 1 contained &gt;6000 viable organisms/g. The ricotta cheese, although temperature-abused, had a titer of 3.6 x 10-6 beta-hemolytic L. monocytogenes cells/g, whereas the semisoft cheeses reached a maximum of 5.6 x 10-6 cells/g. Pure cultures of L. monocytogenes isolated from both types of cheese were found positive by the CAMP test and the DNA probe

scholarly journals Response of Listeria monocytogenes to Disinfection Stress at the Single-Cell and Population Levels as Monitored by Intracellular pH Measurements and Viable-Cell Counts

2009 ◽  
Vol 75 (13) ◽  
pp. 4550-4556 ◽  
Author(s):  
Vicky G. Kastbjerg ◽  
Dennis S. Nielsen ◽  
Nils Arneborg ◽  
Lone Gram
Keyword(s):  
Listeria Monocytogenes ◽  
Single Cell ◽  
Intracellular Ph ◽  
Bacterial Population ◽  
Single Cells ◽  
Viable Cell ◽  
Population Subdivision ◽  
Single Cell Level ◽  
Cell Level ◽  
Cell Counts

ABSTRACT Listeria monocytogenes has a remarkable ability to survive and persist in food production environments. The purpose of the present study was to determine if cells in a population of L. monocytogenes differ in sensitivity to disinfection agents as this could be a factor explaining persistence of the bacterium. In situ analyses of Listeria monocytogenes single cells were performed during exposure to different concentrations of the disinfectant Incimaxx DES to study a possible population subdivision. Bacterial survival was quantified with plate counting and disinfection stress at the single-cell level by measuring intracellular pH (pHi) over time by fluorescence ratio imaging microscopy. pHi values were initially 7 to 7.5 and decreased in both attached and planktonic L. monocytogenes cells during exposure to sublethal and lethal concentrations of Incimaxx DES. The response of the bacterial population was homogenous; hence, subpopulations were not detected. However, pregrowth with NaCl protected the planktonic bacterial cells during disinfection with Incimaxx (0.0015%) since pHi was higher (6 to 6.5) for the bacterial population pregrown with NaCl than for cells grown without NaCl (pHi 5 to 5.5) (P < 0.05). The protective effect of NaCl was reflected by viable-cell counts at a higher concentration of Incimaxx (0.0031%), where the salt-grown population survived better than the population grown without NaCl (P < 0.05). NaCl protected attached cells through drying but not during disinfection. This study indicates that a population of L. monocytogenes cells, whether planktonic or attached, is homogenous with respect to sensitivity to an acidic disinfectant studied on the single-cell level. Hence a major subpopulation more tolerant to disinfectants, and hence more persistent, does not appear to be present.

Note. In Vitro Viability of Bifidobacterium Strains Isolated from Commercial Dairy Products Exposed to Human Gastrointestinal Conditions

2005 ◽  
Vol 11 (4) ◽  
pp. 307-314 ◽  
Author(s):  
M. C. Collado ◽  
Y. Moreno ◽  
E. Hernández ◽  
J. M. Cobo ◽  
M. Hernández
Keyword(s):  
Dairy Products ◽  
Viable Cell ◽  
Human Gastrointestinal Tract ◽  
Cell Counts ◽  
Gastrointestinal Conditions ◽  
Acid Tolerant ◽  
Viable Bacteria ◽  
Selection Of ◽  
Direct Counts

Levels of bifidobacteria contained in commercial fermented milks in Spain were determined by fluorescent techniques. The transit tolerance of probiotic bifidobacteria strains to human gastrointestinal tract (GIT) was assessed in vitro. The number of bifidobacteria in commercial fermented milks declared to contain bifidobacteria varied from 104 to 107 bacteria/m L. Viable cell counts estimated by plating onto selective media were lower than direct counts. Bifidobacteriumstrains analysed showed different survival behaviour. Viable bacteria counts decreased considerably following exposure to gastric juice. As only intrinsic acid resistant cells survive their passage through the human intestine, the selection of acid tolerant strains is necessary for the elaboration of probiotic products. Viability of dairy bifidobacteria is affected by gastrointestinal juices but the majority of tested strains survived well at gastrointestinal conditions. The reason for this may be the low number of viable bifidobacteria contained in commercial dairy products. Adaptation and survival at low pH is likely to determine the efficacy of Bifidobacterium strains both as dairy starters and probiotic microorganisms. This study confirmed the usefulness of fluorescent techniques for a rapid and accurate evaluation of bacterial viability in probiotic products.

scholarly journals Complete genome of the barotolerant Listeria monocytogenes RO15 strain and comparison with other strains isolated from food and food processing environments

2020 ◽  
Author(s):  
Ilhan Cem Duru ◽  
Margarita Andreevskaya ◽  
Pia Laine ◽  
Tone Mari Rode ◽  
Anne Ylinen ◽  
...  
Keyword(s):  
Listeria Monocytogenes ◽  
Foodborne Pathogens ◽  
Genome Analysis ◽  
Food Processing ◽  
Viable Cell ◽  
High Pressure Processing ◽  
Genome Comparison ◽  
Cell Counts ◽  
Reference Type ◽  
Pressure Tolerance

Abstract Background: High pressure processing (HPP; i.e. 100 - 600 MPa pressure depending on product) is a non-thermal preservation technique adopted by the food industry to decrease significantly foodborne pathogens, including Listeria monocytogenes, from food. However, susceptibility towards pressure differs among diverse strains of L. monocytogenes and it is unclear if this is related to their genomic content. Here, we tested the barotolerance of 10 different L. monocytogenes strains, from food and food processing environments and widely used reference type strains, to pressure treatments with 400 and 600 MPa. Genome sequencing and genome comparison of the tested L. monocytogenes strains were performed to investigate the relation between genomic profile and pressure tolerance.Results: None of the tested strains were tolerant to 600 MPa. A reduction of more than 5 log10 was observed for all strains after 1 minute 600 MPa pressure treatment. L. monocytogenes strain RO15 showed no significant reduction in viable cell counts after 400 MPa for 1 minute and was therefore defined as barotolerant. Genome analysis of so far unsequenced L. monocytogenes strain RO15, 2HF33, MB5, AB199, AB120, C7, and RO4 allowed us to compare the gene content of all strains tested. This revealed that the three most pressure tolerant strains had more than one CRISPR system with self-targeting spacers. Furthermore, several anti-CRISPR genes were detected in these strains. Pan-genome analysis showed that 10 prophage genes were significantly associated with the three most barotolerant strains.Conclusions: L. monocytogenes strain RO15 was the most pressure tolerant among the selected strains. Genome comparison suggests that there might be a relationship between prophages and pressure tolerance in L. monocytogenes.

Isolation and Purification of Colicin ECL 12, a Bacteriocin That Inhibits Strains of Escherichia coli O157:H7†

1997 ◽  
Vol 60 (12) ◽  
pp. 1520-1528 ◽  
Author(s):  
WANDA J. LYON ◽  
DENNIS G. OLSON
Keyword(s):  
Escherichia Coli ◽  
Proteolytic Enzymes ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Viable Cell ◽  
Exchange Chromatography ◽  
Isolation And Purification ◽  
E Coli ◽  
Log Reduction ◽  
Cell Counts

A swine fecal isolate, identified as Escherichia coli ECL12, was found to produce an antimicrobial substance designated as colicin ECL12. Colicin ECL12 was inhibitory against 20 strains of E. coli O157:H7 previously isolated from both human and bovine feces. Identification of the producer strain was determined phenotypically by biochemical and morphological tests. Colicin ECL12 was sensitive to several proteolytic enzymes. Adsorption of colicin ECL12 to sensitive cells of E. coli O157:H7 was bactericidal, resulting in a 2 log reduction in viable cell counts. Colicin ECL12 was purified from strain ECL12 by cell extraction and ion-exchange chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of colicin ECL12 resolved a single protein with a molecular weight of approximately 65,000.

Thermal Resistance of Listeria monocytogenes in Dairy Products

1987 ◽  
Vol 50 (7) ◽  
pp. 543-544 ◽  
Author(s):  
J. G. BRADSHAW ◽  
J. T. PEELER ◽  
J. J. CORWIN ◽  
J. M. HUNT ◽  
R. M. TWEDT
Keyword(s):  
Listeria Monocytogenes ◽  
Thermal Resistance ◽  
Dairy Products ◽  
Skim Milk ◽  
Ice Cream ◽  
Milk Samples ◽  
C Value

The thermal resistance of Listeria monocytogenes strain Scott A that had been associated with a recent milkborne outbreak of listeriosis was determined in whole and skim milk, heavy cream, and ice cream mix. L. monocytogenes suspended at concentrations of approximately 1 × 105 cells/ml was heated at temperatures ranging from 52.2 to 79.4°C at various contact times. The D71.7°C values computed for milk samples ranged from 0.9 to 2.7 s. The D7.94°C value in ice cream mix was 0.5 s. The zD value for fluid products ranged from 5.8 to 7.1°C; the zF value for ice cream mix was 7.0°C. The L. monocytogenes suspensions would not survive a proper pasteurization process given to raw dairy products.

KEEPING QUALITY OF DAIRY PRODUCTS OBTAINED AT RETAIL OUTLETS.

1966 ◽  
Vol 29 (7) ◽  
pp. 214-217 ◽  
Author(s):  
B. E. Langlois ◽  
H. E. Randolph ◽  
Nancy M. Crume
Keyword(s):  
Dairy Products ◽  
Flavor Score ◽  
Low Fat ◽  
Milk Samples ◽  
Retail Outlets ◽  
Keeping Quality ◽  
Quality Of Products

Summary A study was made of the bacteriological and keeping quality of low-fat milk, skimmilk, and chocolate flavored milk obtained at retail outlets. Approximately 62% of the low-fat milk samples, 81% of the skimmilk samples, and 93% of the chocolate flavored milk did not have a satisfactory flavor score (36.0 or higher) after storage at 40 ± 2 F for 14 days. The samples ranged in age from 0 to 15 days at time of purchase, the average age being 4.3 days (low-fat milk), 5.3 days (skimmilk), and 5.9 days (chocolate flavored milk). The average days kept at 40 ± 2 F after purchase was 9.5 days (low-fat milk), 7.4 days (skimmilk), and 5.9 days (chocolate flavored milk). Highly significant correlations were observed between: purchase age and initial flavor; days kept and SPC on purchase day, and days kept and SPC after 7 days' storage. The quality of products of an individual brand tended to be similar; whereas, significant quality differences were observed between brands.

scholarly journals Temperature Effect on Listeria Monocytogenes Planktonic Growth and Biofilm-Forming Ability

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Joana Catarina Andrade ◽  
◽  
Rita Bernardo ◽  
António Salvador Barreto ◽  
Telmo Nunes ◽  
...  
Keyword(s):  
Listeria Monocytogenes ◽  
Temperature Effect ◽  
Optical Density ◽  
Crystal Violet ◽  
Biofilm Formation ◽  
Viable Cell ◽  
Crystal Violet Staining ◽  
Cell Counts ◽  
Viable Cells ◽  
Density Results

Listeria Monocytogenes is an important foodborne pathogen with the capacity to grow at low temperatures and the ability to form biofilms. These features are particularly significant to food business operators producing readyto-eat foods with a long refrigerated shelf-life not undergoing any listericidal treatment before consumption. Objectives: This work aims to assess the temperature effect on L. monocytogenes growth in planktonic suspension and in mono-species biofilms. Methods and results: Isothermal planktonic growth at 12o C and 37o C was assayed using viable cell counts and optical density measurements that revealed a strong positive correlation, confirming the reliability of combining both methods to estimate L. monocytogenes concentration. Experimental data were then fitted to Baranyi and Roberts primary predictive model and the estimated growth parameters confirmed that μmax at 37o C (0.375 ± 0.072 log Cfu/ ml/h) was higher than at 120 C (0.054 ± 0.001 log Cfu/ml/h), with identical L. monocytogenes final concentrations which emphasizes its ability to grow at refrigerated temperatures. Experimental results from the isothermal growth assay and ComBase Predictor growth model were similar, with slightly higher estimated μmax (37o C: 0.480 log Cfu/ml/h; 12o C: 0.068 log Cfu/ml/h) in the predictor growth model. The studied strains demonstrated biofilm-forming ability at 12o C, 20o C and 300 C after 5 days of growth. No significant differences in biofilm formation at different temperatures were detected considering viable cell counts values, but when using crystal violet staining optical density results significant differences were found, with the highest formation occurring at 30ºC. A positive strong correlation was found between viable cell counts and crystal violet staining optical density results. In fact, both methods complement each other, because while viable cell counts measures viable cells, crystal violet staining optical density considers total biomass (viable and non-viable cells and extracellular matrix components). Nevertheless, in this work all L. monocytogenes strains revealed to be weak biofilm producers. Conclusion: Overall, this studys results contribute with important initial information on L. monocytogenes growth and biofilm formation to further assist predictive growth modeling in food matrices and environments, also enabling subsequent quantitative microbial risk assessment, to improve pathogen’s control.

Assay of Enterocin AS-48 for Inhibition of Foodborne Pathogens in Desserts

2009 ◽  
Vol 72 (8) ◽  
pp. 1654-1659 ◽  
Author(s):  
PILAR MARTINEZ VIEDMA ◽  
HIKMATE ABRIOUEL ◽  
NABIL BEN OMAR ◽  
ROSARIO LUCAS LÓPEZ ◽  
EVA VALDIVIA ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Listeria Monocytogenes ◽  
Bacillus Cereus ◽  
Proteolytic Activity ◽  
Foodborne Pathogens ◽  
Viable Cell ◽  
Inoculum Size ◽  
Cell Counts

Enterocin AS-48 was tested against Staphylococcus aureus, Bacillus cereus, and Listeria monocytogenes in different kinds of desserts. The highest activity against S. aureus was detected in baker cream. However, in yogurt-type soy-based desserts and in gelatin pudding, AS-48 (175 arbitrary units [AU]/g) reduced viable cell counts of S. aureus by only 1.5 to 1.8 log units at most. The efficacy of AS-48 in puddings greatly depended on inoculum size, and viable S. aureus counts decreased below detection levels within 24 h for inocula lower than 4 to 5.5 log CFU/g. For L. monocytogenes, bacteriocin concentrations of 52.5 to 87.5 AU/g reduced viable counts below detection levels and avoided regrowth of survivors. The lowest activity was detected in yogurt-type desserts. For B. cereus, viable cell counts were reduced below detection levels for bacteriocin concentrations of 52.5 AU/g in instant pudding without soy or by 175 AU/g in the soy pudding. In gelatin pudding, AS-48 (175 AU/g) reduced viable cell counts of B. cereus below detection levels after 8 h at 10°C or after 48 h at 22°C. Bacteriocin addition also inhibited gelatin liquefaction caused by the proteolytic activity of B. cereus.

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