Detection and Enhancement of Ketocarotenoid Accumulation in the Newly Isolated Sarcinoid Green Microalga Chlorosarcinopsis PY02.

The sarcinoid alga PY02 is a newly isolated soil alga native to western Thailand. In this study PY02 is described, the carotenoid profile of the green and red forms of the algal cells are compared, and the effect of nitrogen reduction and media volume on ketocarotenoid production are reported. Partial sequences of the genes from elongation factor Tu (A) and 18S rRNA reveal that the alga is from the genus.

A third mode of surface-associated growth: immobilization of Salmonella enterica serovar Typhimurium modulates the RpoS-directed transcriptional programme.

Although the growth of bacteria has been studied for more than a century, it is only in recent decades that surface-associated growth has received attention. In addition to the well-characterized biofilm and swarming lifestyles, bacteria can also develop as micro-colonies supported by structured environments in both food products and the GI tract. This immobilized mode of growth has not been widely studied.

Spatial distribution of bacterial colonies in a model cheese.

In most ripened cheeses, bacteria are responsible for the ripening process. Immobilized in the cheese matrix, they grow as colonies. Therefore, their distribution as well as the distance between them are of major importance for ripening steps since metabolites diffuse within the cheese matrix.

Effect of storage conditions on the microbial ecology and biochemical stability of cell wall components in brewers' spent grain.

The composition of brewers' spent grain (BSG) makes it susceptible to microbial attack and chemical deterioration. This can constrain its appeal as an industrial feedstock. The current study has monitored the effects of BSG storage as fresh material (20 degrees C), refrigerated and autoclaved, measured against frozen material in relation to microbial proliferation and modification to plant cell wall polysaccharides and component phenolic acids.

Effect of pH, water activity and gel micro-structure, including oxygen profiles and rheological characterization, on the growth kinetics of Salmonella Typhimurium.

In this study, the growth of Salmonella Typhimurium in Tryptic Soy Broth was examined at different pH (4.50-5.50), water activity a(w) (0.

Salmonella must be viable in order to attach to the surface of prepared vegetable tissues.

Aims: The aims of the current study were to explore the site of bacterial attachment to vegetable tissues and to investigate the hypothesis that Salmonella must be living in order to attach to this site(s).

Methods And Results: Scanning electron micrographs of intact potato cells showed that Salm. serotype Typhimurium attached to cell-wall junctions; suggesting a high-level of site selectivity.

Image analysis as a mean to model growth of Escherichia coli O157:H7 in gel cassettes.

Aims: The potential of image analysis for rapid and quantitative determination of the effect of environmental parameters such as temperature and pH on the growth of colonies of Escherichia coli O157:H7 derived from immobilized cells in gel cassettes was investigated.

Methods And Results: The organism was grown in brain heart infusion agar contained within a cassette formed between sheets of PVC film. The medium was adjusted to pH 5, 6 or 7 and incubated at 10, 20, 30 or 40 degrees C.

The lactic acid-induced acid tolerance response in Salmonella enterica serovar Typhimurium induces sensitivity to hydrogen peroxide.

Transcriptome analyses of Salmonella enterica serovar Typhimurium revealed that 15 genes were significantly up-regulated after 2 h of adaptation with lactic acid. cadB was the most highly up-regulated gene and was shown to be an essential component. Lactic acid-adapted cells exhibited sensitivity to hydrogen peroxide, likely due to down-regulation of the OxyR regulon.

The Acetic Acid Tolerance Response induces cross-protection to salt stress in Salmonella typhimurium.

Salmonella typhimurium induces an Acid Tolerance Response (ATR) upon exposure to mildly acidic conditions in order to protect itself against severe acid shock. This response can also induce cross-protection to other stresses such as heat and salt. We investigated whether both the acetic acid induced and lactic acid induced ATR in S.

Modeling the rate of attachment of Listeria monocytogenes, Pantoea agglomerans, and Pseudomonas fluorescens to, and the probability of their detachment from, potato tissue at 10 degrees C.

The rate of attachment of bacteria to, and their subsequent detachment from, the cut surface of raw potato tissue was measured and modeled by using mathematical approaches that allowed detailed objective comparisons of adhesion processes under different conditions. Attachment was rapid and reached equilibrium after contact for 60 min. A new method to measure the probability of detachment was developed and modeled, revealing that the probability of detachment for Pseudomonas fluorescens remained unchanged for contact times between less than 5 s and 60 min.

The antilisterial effect of Leuconostoc carnosum 4010 and leucocins 4010 in the presence of sodium chloride and sodium nitrite examined in a structured gelatin system.

To further enhance biopreservation of meat products, the antilisterial effect of the newly described protective culture Leuconostoc carnosum 4010 and its bacteriocins, leucocins 4010, was examined in the presence of sodium chloride and sodium nitrite in a solid matrix using a structured gelatin system. Interaction between Listeria monocytogenes 4140 and Leuc. carnosum 4010 or the leucocins 4010-resistant mutant L.

Batch growth of Salmonella typhimurium LT2: stoichiometry and factors leading to cessation of growth.

Salmonella typhimurium LT2 was grown in batch culture (trypticase soy broth, with 0.3%(w/v) yeast extract, 1% (w/v) glucose and 0.5% (w/v/) NaCl, 20 degrees C) at a range of initial pH (4.

Salmonella enterica serovar Typhimurium and Listeria monocytogenes acid tolerance response induced by organic acids at 20 degrees C: optimization and modeling.

An acid tolerance response (ATR) has been demonstrated in Listeria monocytogenes and Salmonella enterica serovar Typhimurium in response to low pH poised (i.e., adapted) with acetic or lactic acids at 20 degrees C and modeled by using dynamic differential equations.

Modelling microbial growth in structured foods: towards a unified approach.

Historically, the ability of foods to support the growth of spoilage organisms and food-borne pathogens has been assessed by inoculating a food with an organism of interest, and following its growth over a period of time. Information gained from such challenge tests, together with knowledge of the organoleptic stability of the product, can then be used to determine an appropriate shelf-life for the food. Whilst this approach may be seen as the "gold-standard" of microbiological assessment of food, it is both time-consuming and costly.

Microgradients in bacterial colonies: use of fluorescence ratio imaging, a non-invasive technique.

Fluorescence ratio imaging is a non-invasive technique for studying the formation of microgradients in immobilised bacterial colonies. These gradients can be quantified easily when combined with the gel cassette system designed at the Institute of Food Research, Norwich, UK. Colonies of Lactobacillus curvatus were observed using this technique and relevant pH gradients were present when the colonies reached a diameter of about 100 microm.

Adenylates and adenylate-energy charge in submerged and planktonic cultures of Salmonella enteritidis and Salmonella typhimurium.

Adenine nucleotide values and adenylate energy charge (AEC) were measured during the growth of Salmonella enteritidis and Salmonella typhimurium as submerged colonies in agarose gel and gelatin gel, and as planktonic cells in broth. Growth in all three systems showed similar trends with a ten-fold decrease in total adenylate pool during exponential growth, before attaining a fairly stable value throughout stationary phase. AEC values were generally low, (approximately 0.

The microstructure and distribution of micro-organisms within mature Serra cheese.

The distribution of micro-organisms in mature Serra, a traditional Portuguese cheese made from unpasteurised ewes' milk without added starter culture, was examined by light microscopy and electron microscopy. Four populations of micro-organisms were recognized according to their position within the cheese: (i) those present as apparently axenic colonies within the curd matrix; (ii) bacteria growing along curd junctions; (iii) yeasts and bacteria present in the smear on the surface of the cheese and (iv) bacteria found in cracks which penetrated the outer part of the cheese from the rind. Two types of crystals were observed, together with contaminants of vegetable origin and somatic cells originating from the milk.

Water availability and the survival of Salmonella typhimurium in porous systems.

The survival of Salmonella Typhimurium LT2 in randomly packed beds of glass beads, microporous silica particles and Sephadex microspheres is examined. It is shown that the decrease in the percentage cell recovery in these porous materials at reduced water content is not correlated with the global water activity as determined by conventional vapour pressure measurements but rather with the osmotic shock induced by the sudden redistribution of water and air among the microscopic pores in the matrix surrounding the cells. For this reason the bacterial survival and growth data correlates best with physical measurements, such as NMR and electrical conductivity, which are sensitive to the microscopic air-water distribution.

The effects of growth dynamics upon pH gradient formation within and around subsurface colonies of Salmonella typhimurium.

pH measurements made in and around submerged colonies of Salmonella typhimurium grown within a model gelatin gel system using pH-sensitive micro- and macroelectrodes indicated some pH heterogeneity occurring in and around the bacterial colony. Inoculation density, initial pH and glucose concentration were all found to influence colony diameter and metabolism of Salmonella colonies. Colony growth in the presence of glucose, at pH 7.

The effect of transient temperatures on the growth of Salmonella typhimurium LT2 in gelatin gel.

The growth of colonies of Salmonella typhimurium derived from single immobilised cells was studied while subjected to constant and sinusoidally-varying temperatures. The bacteria grew in microbiological culture media adjusted to different pH and sodium chloride (NaCl) concentration and solidified with gelatin that was contained within a cassette formed between sheets of PVC film that allowed gaseous exchange. At pH 7.

The effect of transient temperatures on the growth of Salmonella typhimurium LT2. II: Excursions outside the growth region.

The effect of fluctuating temperatures on microbial growth is important in the passage of foods from production to consumption. Suspensions of Salmonella typhimurium have been subjected to sinusoidally time-varying temperatures of periods from 60 to 240 min between 4 degrees and 22 degrees C, that is within and below the growth temperature range. The suspensions were prepared with two concentrations of sodium chloride and adjusted to two different values of pH.

Growth of food-borne pathogenic bacteria in oil-in-water emulsions: II--Effect of emulsion structure on growth parameters and form of growth.

The growth rates and yields of Listeria monocytogenes and Yersinia enterocolitica were determined in liquid culture media, and in model oil-in-water emulsions that contained 30, 70 or 83% (v/v) hexadecane. In emulsions with a mean droplet size of 2 microns containing 83% (v/v) hexadecane, the growth of both organisms resulted in decreased yields. Additionally, in these emulsions adjusted to pH 5.

Growth of food-borne pathogenic bacteria in oil-in-water emulsions: I--Methods for investigating the form of growth.

Methods are presented for investigating the site and form of growth of bacteria in model oil-in-water emulsions and in dairy cream. Following growth of the bacteria, the continuous aqueous phase is gelled using agarose and the oil phase removed using a mixture of chloroform and methanol. Using this method, the authors have found that Listeria monocytogenes, Salmonella typhimurium and Yersinia enterocolitica grow in the form of colonies in concentrated oil-in-water emulsions.

The effect of step changes in sucrose concentration on the growth of Salmonella typhimurium LT2.

Water activity is a method of preservation that can affect microbial growth in foods and that may fluctuate during their processing, distribution and storage. Sucrose has been used to change the water activity of microbiological culture media. Suspensions of Salmonella typhimurium LT2 in the exponential phase of growth have been subjected to step changes in sucrose concentration at 20 degrees C.

The effect of transient temperatures on the growth of Salmonella typhimurium LT2. I: Cycling within the growth region.

The effect of fluctuating temperatures on microbial growth is important in the passage of foods through the food chain. Suspensions of Salmonella typhimurium were subjected to sinusoidally time-varying temperatures of periods from 40 to 480 min within their growth temperature range. The change in the numbers of viable bacteria was measured with time and the experimental growth curves and average generation times compared with predictions based on isothermal growth data.