scholarly journals Modeling the Lag Period and Exponential Growth of Listeria monocytogenes under Conditions of Fluctuating Temperature and Water Activity Values

2010 ◽  
Vol 76 (9) ◽  
pp. 2908-2915 ◽  
Author(s):  
Marina Muñoz-Cuevas ◽  
Pablo S. Fernández ◽  
Susan George ◽  
Carmen Pin
Keyword(s):  
Water Activity ◽  
Environmental Conditions ◽  
Exponential Growth ◽  
Sudden Change ◽  
Growth Conditions ◽  
Lag Phase ◽  
Fluctuating Temperature ◽  
Lag Period ◽  
Work Done ◽  
Good Agreement

ABSTRACT The dynamic model for the growth of a bacterial population described by Baranyi and Roberts (J. Baranyi and T. A. Roberts, Int. J. Food Microbiol. 23:277-294, 1994) was applied to model the lag period and exponential growth of L isteria monocytogenes under conditions of fluctuating temperature and water activity (aw) values. To model the duration of the lag phase, the dependence of the parameter h 0, which quantifies the amount of work done during the lag period, on the previous and current environmental conditions was determined experimentally. This parameter depended not only on the magnitude of the change between the previous and current environmental conditions but also on the current growth conditions. In an exponentially growing population, any change in the environment requiring a certain amount of work to adapt to the new conditions initiated a lag period that lasted until that work was finished. Observations for several scenarios in which exponential growth was halted by a sudden change in the temperature and/or aw were in good agreement with predictions. When a population already in a lag period was subjected to environmental fluctuations, the system was reset with a new lag phase. The work to be done during the new lag phase was estimated to be the workload due to the environmental change plus the unfinished workload from the uncompleted previous lag phase.

The value of Electron Microscope studies of imperfect natural diamonds

1990 ◽  
Vol 48 (4) ◽  
pp. 194-195
Author(s):  
J C Walmsley ◽  
A R Lang
Keyword(s):  
Electron Microscope ◽  
Classification Scheme ◽  
Natural Diamond ◽  
Sudden Change ◽  
Growth Conditions ◽  
Diamond Growth ◽  
Major Constituent ◽  
Natural Diamonds ◽  
Type Ia ◽  
Platelet Defects

Interest in the defects and impurities in natural diamond, which are found in even the most perfect stone, is driven by the fact that diamond growth occurs at a depth of over 120Km. They display characteristics associated with their origin and their journey through the mantle to the surface of the Earth. An optical classification scheme for diamond exists based largely on the presence and segregation of nitrogen. For example type Ia, which includes 98% of all natural diamonds, contain nitrogen aggregated into small non-paramagnetic clusters and usually contain sub-micrometre platelet defects on {100} planes. Numerous transmission electron microscope (TEM) studies of these platelets and associated features have been made e.g. . Some diamonds, however, contain imperfections and impurities that place them outside this main classification scheme. Two such types are described.First, coated-diamonds which possess gem quality cores enclosed by a rind that is rich in submicrometre sized mineral inclusions. The transition from core to coat is quite sharp indicating a sudden change in growth conditions, Figure 1. As part of a TEM study of the inclusions apatite has been identified as a major constituent of the impurity present in many inclusion cavities, Figure 2.

Validation and Analysis of Modeled Predictions of Growth of Bacillus cereus Spores in Boiled Rice

2000 ◽  
Vol 63 (2) ◽  
pp. 268-272 ◽  
Author(s):  
DANA M. McELROY ◽  
LEE-ANN JAYKUS ◽  
PEGGY M. FOEGEDING
Keyword(s):  
Growth Rate ◽  
Bacillus Cereus ◽  
Exponential Growth ◽  
Generation Time ◽  
Time Lag ◽  
Lag Phase ◽  
Exponential Growth Rate ◽  
Phase Duration ◽  
Margin Of Safety ◽  
Fail Safe

The growth of psychrotrophic Bacillus cereus 404 from spores in boiled rice was examined experimentally at 15, 20, and 30°C. Using the Gompertz function, observed growth was modeled, and these kinetic values were compared with kinetic values for the growth of mesophilic vegetative cells as predicted by the U.S. Department of Agriculture's Pathogen Modeling Program, version 5.1. An analysis of variance indicated no statistically significant difference between observed and predicted values. A graphical comparison of kinetic values demonstrated that modeled predictions were “fail safe” for generation time and exponential growth rate at all temperatures. The model also was fail safe for lag-phase duration at 20 and 30°C but not at l5°C. Bias factors of 0.55, 0.82, and 1.82 for generation time, lag-phase duration, and exponential growth rate, respectively, indicated that the model generally was fail safe and hence provided a margin of safety in its growth predictions. Accuracy factors of 1.82, 1.60, and 1.82 for generation time, lag-phase duration, and exponential growth rate, respectively, quantitatively demonstrated the degree of difference between predicted and observed values. Although the Pathogen Modeling Program produced reasonably accurate predictions of the growth of psychrotrophic B. cereus from spores in boiled rice, the margin of safety provided by the model may be more conservative than desired for some applications. It is recommended that if microbial growth modeling is to be applied to any food safety or processing situation, it is best to validate the model before use. Once experimental data are gathered, graphical and quantitative methods of analysis can be useful tools for evaluating specific trends in model prediction and identifying important deviations between predicted and observed data.

scholarly journals Sleeping ribosomes: bacterial signaling triggers RaiA mediated persistence to aminoglycosides

2020 ◽  
Author(s):  
Manon Lang ◽  
Evelyne Krin ◽  
Chloé Korlowski ◽  
Odile Sismeiro ◽  
Hugo Varet ◽  
...  
Keyword(s):  
Sucrose Gradient ◽  
Gradient Analysis ◽  
Cell Formation ◽  
Fold Increase ◽  
Growth Conditions ◽  
Lag Phase ◽  
Bacterial Signaling ◽  
Tryptophan Degradation ◽  
70S Ribosome ◽  
Persistent Cell

AbstractIndole is a small molecule derived from tryptophan degradation and proposed to be involved in bacterial signaling. We find that indole secretion is induced by sublethal tobramycin concentrations and increases persistence to aminoglycosides in V. cholerae. Indole transcriptomics showed strongly increased expression of raiA, a ribosome associated factor. Deletion of raiA abolishes the appearance of indole dependent persisters to aminoglycosides, while its overexpression leads to 100-fold increase of persisters, and a reduction in lag phase, evocative of increased active 70S ribosome content, which was confirmed by sucrose gradient analysis. We propose that, under stress conditions, inactive 70S ribosomes are associated with RaiA to be stored and rapidly reactivated when growth conditions become favorable again, in a mechanism different than ribosome hibernation. Our results point to an active process of persistent cell formation, through ribosome protection during translational stress and relief upon antibiotic removal. Translation is a universal process, and these results could help elucidate a mechanism of persistence formation in a controlled, thus inducible way.

scholarly journals Temperature Robust PCA Based Stress Monitoring Approach

2016 ◽  
Vol 713 ◽  
pp. 288-292 ◽  
Author(s):  
Jabid Quiroga ◽  
John Quiroga ◽  
Luis Mujica ◽  
Rodolfo Villamizar ◽  
Magda Ruiz
Keyword(s):  
Statistical Model ◽  
Numerical Simulations ◽  
Environmental Conditions ◽  
Guided Wave ◽  
Stress Monitoring ◽  
Robust Pca ◽  
Different Temperatures ◽  
Stress States ◽  
Good Agreement

In this paper, a guided wave temperature robust PCA-based stress monitoring methodology is proposed. It is based on the analysis of the longitudinal guided wave propagating along the path under stress. Slight changes in the wave are detected by means of PCA via statistical T2 and Q indices. Experimental and numerical simulations of the guided wave propagating in material under different temperatures have shown significant variations in the amplitude and the velocity of the wave. This condition can jeopardize the discrimination of the different stress scenarios detected by the PCA indices. Thus, it is proposed a methodology based on an extended knowledge base, composed by a PCA statistical model for different discrete temperatures to produce a robust classification of stress states under variable environmental conditions. Experimental results have shown a good agreement between the predicted scenarios and the real ones

Modeling the Effect of Water Activity, pH, and Temperature on the Probability of Enterotoxin A Production by Staphylococcus aureus

2016 ◽  
Vol 79 (1) ◽  
pp. 148-152 ◽  
Author(s):  
TIAN DING ◽  
YAN-YAN YU ◽  
CHENG-AN HWANG ◽  
QING-LI DONG ◽  
SHI-GUO CHEN ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Water Activity ◽  
Storage Temperature ◽  
Probability Model ◽  
Toxin Production ◽  
Factors Affecting ◽  
Model Predictions ◽  
And Storage ◽  
Storage Temperatures ◽  
Good Agreement

ABSTRACT The objectives of this study were to develop a probability model of Staphylococcus aureus enterotoxin A (SEA) production as affected by water activity (aw), pH, and temperature in broth and assess its applicability for milk. The probability of SEA production was assessed in tryptic soy broth using 24 combinations of aw (0.86 to 0.99), pH (5.0 to 7.0), and storage temperature (10 to 30°C). The observed probabilities were fitted with a logistic regression to develop a probability model. The model had a concordant value of 97.5% and concordant index of 0.98, indicating that the model satisfactorily describes the probability of SEA production. The model showed that aw, pH, and temperature were significant factors affecting the probability of toxin production. The model predictions were in good agreement with the observed values obtained from milk. The model may help manufacturers in selecting product pH and aw and storage temperatures to prevent SEA production.

Correlation of Water Activity and Other Environmental Conditions with Repeated Detection of Salmonella Contamination on Poultry Farms

1992 ◽  
Vol 36 (3) ◽  
pp. 664 ◽  
Author(s):  
O. O. Opara ◽  
L. E. Carr ◽  
E. Russek-Cohen ◽  
C. R. Tate ◽  
E. T. Mallinson ◽  
...  
Keyword(s):  
Water Activity ◽  
Environmental Conditions ◽  
Poultry Farms

Analysis of the lag phase to exponential growth transition by incorporating inoculum characteristics

2011 ◽  
Vol 28 (4) ◽  
pp. 656-666 ◽  
Author(s):  
A.J. Verhulst ◽  
A.M. Cappuyns ◽  
E. Van Derlinden ◽  
K. Bernaerts ◽  
J.F. Van Impe
Keyword(s):  
Exponential Growth ◽  
Lag Phase

scholarly journals Abiotic Stresses Shift Belowground Populus-Associated Bacteria Toward a Core Stress Microbiome

mSystems ◽  
2018 ◽  
Vol 3 (1) ◽  
Author(s):  
Collin M. Timm ◽  
Kelsey R. Carter ◽  
Alyssa A. Carrell ◽  
Se-Ran Jun ◽  
Sara S. Jawdy ◽  
...  
Keyword(s):  
Plant Growth ◽  
Environmental Conditions ◽  
Bacterial Communities ◽  
Abiotic Stresses ◽  
Growth Conditions ◽  
Plant Host ◽  
Associated Bacteria ◽  
Poplar Trees

The identification of a common “stress microbiome” indicates tightly controlled relationships between the plant host and bacterial associates and a conserved structure in bacterial communities associated with poplar trees under different growth conditions. The ability of the microbiome to buffer the plant from extreme environmental conditions coupled with the conserved stress microbiome observed in this study suggests an opportunity for future efforts aimed at predictably modulating the microbiome to optimize plant growth.

scholarly journals When Unity Is Strength: The Strategies Used by Chlamydomonas to Survive Environmental Stresses

Cells ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 1307 ◽  
Author(s):  
Félix de Carpentier ◽  
Stéphane D. Lemaire ◽  
Antoine Danon
Keyword(s):  
Environmental Conditions ◽  
Wide Spectrum ◽  
Optimal Growth ◽  
Growth Conditions ◽  
Mild Stress ◽  
Unicellular Alga ◽  
Unicellular Organism ◽  
Unicellular Green Alga ◽  
Scientific Fields ◽  
Do So

The unicellular green alga Chlamydomonas reinhardtii is a valuable model system to study a wide spectrum of scientific fields, including responses to environmental conditions. Most studies are performed under optimal growth conditions or under mild stress. However, when environmental conditions become harsher, the behavior of this unicellular alga is less well known. In this review we will show that despite being a unicellular organism, Chlamydomonas can survive very severe environmental conditions. To do so, and depending on the intensity of the stress, the strategies used by Chlamydomonas can range from acclimation to the formation of multicellular structures, or involve programmed cell death.

Development of System for High Quality Wood Grain Design

2011 ◽  
Author(s):  
Takuya Mori ◽  
Satoshi Shibasaki ◽  
Hideki Aoyama
Keyword(s):  
Computer Graphics ◽  
Tree Growth ◽  
Wood Surface ◽  
Environmental Conditions ◽  
Tree Species ◽  
Growth Conditions ◽  
High Quality ◽  
New Approach ◽  
Conventional Methods ◽  
Wood Grain

Various approaches for generating woodgrain patterns using computer graphics have been proposed so far. However, it is difficult to reproduce real woodgrain patterns using such conventional methods. In this paper, a new approach for generating woodgrain patterns is proposed. Virtual trees are generated by simulating tree growth in consideration of environmental conditions. Moreover, fine tree tissues and reflection properties at the wood surface are modeled. By applying these modeled factors, more diverse and accurate woodgrain patterns can be generated. With this approach, various types of virtual trees can be obtained by changing growth conditions such as period and location of growth or form of tissue in trees without the need to reset complicated parameters of each tree species. After this, the virtual trees can be cut at arbitrary areas, thus allowing a variety of woodgrain patterns to be generated by easy parameter setup.

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