Limits...
Bacterial Colonies in Solid Media and Foods: A Review on Their Growth and Interactions with the Micro-Environment.

Jeanson S, Floury J, Gagnaire V, Lortal S, Thierry A - Front Microbiol (2015)

Bottom Line: The following conclusions have been brought to light.By studying the literature, we concluded that there systematically exists a threshold that distinguishes micro-colonies (radius < 100-200 μm) from macro-colonies (radius >200 μm).In conclusion, the impact of immobilization is predominant for macro-colonies in comparison with micro-colonies.

View Article: PubMed Central - PubMed

Affiliation: INRA, UMR1253, Science and Technology of Milk and Eggs Rennes, France ; AGROCAMPUS OUEST, UMR1253, Science and Technology of Milk and Eggs Rennes, France.

ABSTRACT
Bacteria, either indigenous or added, are immobilized in solid foods where they grow as colonies. Since the 80's, relatively few research groups have explored the implications of bacteria growing as colonies and mostly focused on pathogens in large colonies on agar/gelatine media. It is only recently that high resolution imaging techniques and biophysical characterization techniques increased the understanding of the growth of bacterial colonies, for different sizes of colonies, at the microscopic level and even down to the molecular level. This review covers the studies on bacterial colony growth in agar or gelatine media mimicking the food environment and in model cheese. The following conclusions have been brought to light. Firstly, under unfavorable conditions, mimicking food conditions, the immobilization of bacteria always constrains their growth in comparison with planktonic growth and increases the sensibility of bacteria to environmental stresses. Secondly, the spatial distribution describes both the distance between colonies and the size of the colonies as a function of the initial level of population. By studying the literature, we concluded that there systematically exists a threshold that distinguishes micro-colonies (radius < 100-200 μm) from macro-colonies (radius >200 μm). Micro-colonies growth resembles planktonic growth and no pH microgradients could be observed. Macro-colonies growth is slower than planktonic growth and pH microgradients could be observed in and around them due to diffusion limitations which occur around, but also inside the macro-colonies. Diffusion limitations of milk proteins have been demonstrated in a model cheese around and in the bacterial colonies. In conclusion, the impact of immobilization is predominant for macro-colonies in comparison with micro-colonies. However, the interaction between the colonies and the food matrix itself remains to be further investigated at the microscopic scale.

No MeSH data available.


Related in: MedlinePlus

Representation of the colony and its surrounding “living space” (the area within which the colony is active) with the two respective radii Rcol and Rbnd; d is the distance between two neighboring colonies. Adapted from Malakar et al. (2002a) and Wimpenny (1992).
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Figure 1: Representation of the colony and its surrounding “living space” (the area within which the colony is active) with the two respective radii Rcol and Rbnd; d is the distance between two neighboring colonies. Adapted from Malakar et al. (2002a) and Wimpenny (1992).

Mentions: When considering the dimensions of a colony, there are two radii of particular importance: the colony radius from the center of the colony to its periphery (Rcol), and the boundary radius from the center of the colony to the limit of its influence on the medium (Rbnd) (Malakar et al., 2002a). Figure 1 illustrates these two radii: the colony itself is defined by the radius (Rcol) and its “living space” is defined as the region around the colony (Rbnd) within which the activity of the bacterial cells is measurable (dashed line), for example by the consumption of substrates and/or production of end-products. The larger the colony (large Rcol), the higher the activity of the colony, the greater the “living spaces” (large Rbnd). Furthermore, the larger the radius Rbnd, the greater the distance for the substrate to diffuse to reach the colony. The value of Rbnd at the moment of an inoculation of 1 cfu/ml was estimated to be five times longer that for an inoculation of 100 cfu/ml (Malakar et al., 2002a).


Bacterial Colonies in Solid Media and Foods: A Review on Their Growth and Interactions with the Micro-Environment.

Jeanson S, Floury J, Gagnaire V, Lortal S, Thierry A - Front Microbiol (2015)

Representation of the colony and its surrounding “living space” (the area within which the colony is active) with the two respective radii Rcol and Rbnd; d is the distance between two neighboring colonies. Adapted from Malakar et al. (2002a) and Wimpenny (1992).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664638&req=5

Figure 1: Representation of the colony and its surrounding “living space” (the area within which the colony is active) with the two respective radii Rcol and Rbnd; d is the distance between two neighboring colonies. Adapted from Malakar et al. (2002a) and Wimpenny (1992).
Mentions: When considering the dimensions of a colony, there are two radii of particular importance: the colony radius from the center of the colony to its periphery (Rcol), and the boundary radius from the center of the colony to the limit of its influence on the medium (Rbnd) (Malakar et al., 2002a). Figure 1 illustrates these two radii: the colony itself is defined by the radius (Rcol) and its “living space” is defined as the region around the colony (Rbnd) within which the activity of the bacterial cells is measurable (dashed line), for example by the consumption of substrates and/or production of end-products. The larger the colony (large Rcol), the higher the activity of the colony, the greater the “living spaces” (large Rbnd). Furthermore, the larger the radius Rbnd, the greater the distance for the substrate to diffuse to reach the colony. The value of Rbnd at the moment of an inoculation of 1 cfu/ml was estimated to be five times longer that for an inoculation of 100 cfu/ml (Malakar et al., 2002a).

Bottom Line: The following conclusions have been brought to light.By studying the literature, we concluded that there systematically exists a threshold that distinguishes micro-colonies (radius < 100-200 μm) from macro-colonies (radius >200 μm).In conclusion, the impact of immobilization is predominant for macro-colonies in comparison with micro-colonies.

View Article: PubMed Central - PubMed

Affiliation: INRA, UMR1253, Science and Technology of Milk and Eggs Rennes, France ; AGROCAMPUS OUEST, UMR1253, Science and Technology of Milk and Eggs Rennes, France.

ABSTRACT
Bacteria, either indigenous or added, are immobilized in solid foods where they grow as colonies. Since the 80's, relatively few research groups have explored the implications of bacteria growing as colonies and mostly focused on pathogens in large colonies on agar/gelatine media. It is only recently that high resolution imaging techniques and biophysical characterization techniques increased the understanding of the growth of bacterial colonies, for different sizes of colonies, at the microscopic level and even down to the molecular level. This review covers the studies on bacterial colony growth in agar or gelatine media mimicking the food environment and in model cheese. The following conclusions have been brought to light. Firstly, under unfavorable conditions, mimicking food conditions, the immobilization of bacteria always constrains their growth in comparison with planktonic growth and increases the sensibility of bacteria to environmental stresses. Secondly, the spatial distribution describes both the distance between colonies and the size of the colonies as a function of the initial level of population. By studying the literature, we concluded that there systematically exists a threshold that distinguishes micro-colonies (radius < 100-200 μm) from macro-colonies (radius >200 μm). Micro-colonies growth resembles planktonic growth and no pH microgradients could be observed. Macro-colonies growth is slower than planktonic growth and pH microgradients could be observed in and around them due to diffusion limitations which occur around, but also inside the macro-colonies. Diffusion limitations of milk proteins have been demonstrated in a model cheese around and in the bacterial colonies. In conclusion, the impact of immobilization is predominant for macro-colonies in comparison with micro-colonies. However, the interaction between the colonies and the food matrix itself remains to be further investigated at the microscopic scale.

No MeSH data available.


Related in: MedlinePlus