Determining specific growth rates in different regions of
            <b>
              <i>Salmonella typhimurium</i>
            </b>
            colonies

Mckay, A. L.; Peters, Adrian; Wimpenny, J. W. T.

doi:10.1046/j.1472-765x.1997.00354.x

Cited by 31 publications

(21 citation statements)

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“…A growing colony may be constituted of cells in different physiological states. Cells in the exponential growth phase were shown previously to grow at the outer layer of the colony (21), in contact with the matrix. This outer layer is thus most likely highly metabolically active.…”

Section: Discussionmentioning

confidence: 93%

Spatial Distribution of Bacterial Colonies in a Model Cheese

Jeanson

Chadœuf

Madec

et al. 2011

Appl Environ Microbiol

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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. No data are available to date about the spatial distribution of bacterial colonies in cheese. This is the first study to model the distribution of bacterial colonies in a food-type matrix using nondestructive techniques. We compared (i) the mean theoretical three-dimensional (3D) distances between colonies calculated on the basis of inoculation levels and considering colony distribution to be random and (ii) experimental measurements using confocal microscopy photographs of fluorescent colonies of a Lactococcus lactis strain producing green fluorescent protein (GFP) inoculated, at different levels, into a model cheese made by ultrafiltration (UF). Enumerations showed that the final numbers of cells were identical whatever the inoculation level (10 4 to 10 7 CFU/g). Bacterial colonies were shown to be randomly distributed, fitting Poisson's model. The initial inoculation level strongly influenced the mean distances between colonies (from 25 m to 250 m) and also their mean diameters. The lower the inoculation level, the larger the colonies were and the further away from each other. Multiplying the inoculation level by 50 multiplied the interfacial area of exchange with the cheese matrix by 7 for the same cell biomass. We finally suggested that final cell numbers should be discussed together with inoculation levels to take into account the distribution and, consequently, the interfacial area of colonies, which can have a significant influence on the cheese-ripening process on a microscopic scale.During cheese making, regardless of the cheese type, bacteria are immobilized in the curd during the coagulation step. It is generally accepted that 90% of the bacteria present in the milk are retained, trapped in the curd, while only 10% are lost in the whey during draining (16). In cheeses made by ultrafiltration (UF), the draining step is absent, and 100% of the cells are then retained in the curd. In any case, after immobilization by coagulation, each inoculated bacterial cell is assumed to grow, generating a colony inside the curd. Colonies are then spread within the cheese curd, and they interact with the cheese matrix during ripening. Consequently, the ripening process must take place on a microscopic scale around colonies. Only studies showing microscopic examinations of bacterial colonies in cheese either by electronic microscopy (24) or, more recently, by confocal laser scanning microscopy (7, 19) have been reported.The ripening process (proteolysis, lipolysis, amino acid catabolism, and the production of organic acids, etc.) relies on the metabolic activities of bacterial colonies, leading to the formation of flavors and textures of cheese (11,25). So far, ripening has always been described with average processes on the che...

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Section: Discussionmentioning

confidence: 93%

Spatial Distribution of Bacterial Colonies in a Model Cheese

Jeanson

Chadœuf

Madec

et al. 2011

Appl Environ Microbiol

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“…Alternative methodologies are available, such as the use of image analysis techniques for determination of growth rates in situ [37] and of £uorescence-labelled ribosomal probes to quantify cellular RNA, which in turn can be related to growth rate [42]. Alternative methodologies are available, such as the use of image analysis techniques for determination of growth rates in situ [37] and of £uorescence-labelled ribosomal probes to quantify cellular RNA, which in turn can be related to growth rate [42].…”

Section: Discussionmentioning

confidence: 99%

A model for bacterial conjugal gene transfer on solid surfaces

Lagido

Wilson

Glover

et al. 2003

FEMS Microbiology Ecology

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Quantitative models of bacterial conjugation are useful tools in environmental risk assessment and in studies of the ecology and evolution of bacterial communities. We constructed a mathematical model for gene transfer between bacteria growing on a solid surface. The model considers that donor and recipient cells will form separate colonies, which grow exponentially until nutrient exhaustion. Conjugation occurs when donor and recipient colonies meet, all recipient cells becoming transconjugants instantly, after which they act as donors. The model was tested theoretically by computer simulations that followed the histories of individual bacterial colonies and was validated for initial surface coverage of 60% or less, where confluent growth does not occur. Model predictions of final number of donors, recipients and transconjugants were tested experimentally using a filter mating system with two isogenic strains of Pseudomonas fluorescens MON787 acting as donor and recipient of plasmid RP4. Experimental trends resulting from varying donor and recipient inoculum numbers and donor:recipient ratios were well described by the model, although it often overestimated conjugation by 0.5-2 orders of magnitude. Predictions were greatly improved, generally to within half a log unit of experimental values, by consideration of the time for conjugative transfer. The model demonstrates the relationship between spatial separation of cells and nutrient availability on numbers of transconjugants. By providing a mechanistic approach to the study conjugation on surfaces, the model may contribute to the study of gene transfer in natural environments.

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“…The biomass of the population increased in proportion to the supply rate of the substrate. The planktonic culture had a maximum growth rate in the present system of m 0·96 h −1 while bacteria on membranes grew with The slower growth and decrease in growth rate in the biofilm at least one generation before reaching the stationary phase may be due to the restricted availability of nutrients (Wimpenny 1990;McKay et al 1997) The amount of nutrient diffusing from the solid substrate into the biofilm diminishes with the depletion of the substrate. At the same time the population of the biofilm is increasing.…”

Section: Growth Of Escherichia Coli Dependent On the Glucose Concentrmentioning

confidence: 95%

Generation of a reproducible nutrient‐depleted biofilm of Escherichia coli and Burkholderia cepacia

Bühler

Ballestero

Desai

et al. 1998

Journal of Applied Microbiology

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An in vitro method of growing bacteria as a defined nutrient‐depleted biofilm is proposed. The medium was defined nutritionally in terms of the quantitative composition and by the total amount of nutrient required to achieve a defined population size. Escherichia coli and Burkholderia cepacia were incubated on a filter support placed on a defined volume of solid medium. The change of biomass of the biofilm population was compared with the change in a planktonic culture. The size of the population in stationary phase was proportional to the concentration of limiting substrate up to 40 μmol cm−2 glucose for E. coli and up to 2·7 × 10−9 mol cm−2 iron for B. cepacia. Escherichia coli growing exponentially had a growth rate of μ = 0·30 h−1 in a biofilm and μ = 0·96 h−1 in planktonic culture. The growth rate, μ, for exponentially growing B. cepacia in a biofilm was 1·12 h−1 and in planktonic culture 0·78 h−1. This method allows the limitation of the size of a biofilm population to a chosen value.

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Determining specific growth rates in different regions of Salmonella typhimurium colonies

Cited by 31 publications

References 0 publications

Spatial Distribution of Bacterial Colonies in a Model Cheese

Spatial Distribution of Bacterial Colonies in a Model Cheese

A model for bacterial conjugal gene transfer on solid surfaces

Generation of a reproducible nutrient‐depleted biofilm of Escherichia coli and Burkholderia cepacia

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