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

Growth/no growth regions of Salmonella Typhimurium in TSB (tryptic soy broth) at 20°C as a function of pH and NaCl concentrations, with gelatine concentrations of 0 and 50 g/l. Adapted from Theys et al. (2010).
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Figure 3: Growth/no growth regions of Salmonella Typhimurium in TSB (tryptic soy broth) at 20°C as a function of pH and NaCl concentrations, with gelatine concentrations of 0 and 50 g/l. Adapted from Theys et al. (2010).

Mentions: The growth of a strain of Salmonella enterica subsp. enterica serotype Typhimurium (named S. Typhimurium thereafter) in gelatine medium was compared to its growth in broth, at different conditions of pH and NaCl (Brocklehurst et al., 1995). The results show that S. Typhimurium behaves the same when growing in colonies and in a planktonic culture when under optimal conditions (pH = 7 and NaCl concentration of 0.5%). However, the generation time t (t = log2/μ where μ is the growth rate) was increased by a factor between 1.3 and 2 in the more stressful conditions (pH = 5 and NaCl concentration of 3.5%). The growth rates of this bacterial strain were thus ordered as follow: μplanktonic > μsubmerged > μsurface regardless of the aw when the NaCl concentration was 0.5%, and regardless of the NaCl concentration for maximum aw (Brocklehurst et al., 1997). The maximum viable cell counts were less affected by a low value of aw reduced by high sucrose and NaCl concentrations if the colony was submerged rather than on the surface. An explanation could be that the substrates are only accessible through the small area of the underside of surface colonies, whilst it is accessible all around the colony on a bigger area when submerged. By comparing a strain of S. Typhimurium growing as submerged colonies or in planktonic culture, it was shown that the aw was the most influential parameter on the growth rates (Theys et al., 2008). However, decreasing aw by increasing NaCl concentration was relatively more harmful to the growth of colonies, because of the combined effect on osmotic pressure, than by increasing gelatine concentrations of the media (Theys et al., 2010). In agreement with the latter, a lower growth rate of growth was observed in planktonic cultures than in submerged colonies of a strain of S. Typhimurium and the growth in colonies increased its sensitivity to the inhibition exerted by oregano oil (Skandamis et al., 2000). Surprisingly, the growth rate of submerged colonies of S. Typhimurium was found lower in broth than in agar medium, but lower in gelatine medium than in broth (Walker et al., 1998). Furthermore, when the growth rate was not affected by the immobilization of bacteria, the lag phase was increased in comparison to planktonic growth (Knudsen et al., 2012; Nielsen et al., 2013). Figure 3 is an example of the detrimental effect of immobilization of bacteria on their growth when under severe conditions such as low pH and high concentration of NaCl.


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)

Growth/no growth regions of Salmonella Typhimurium in TSB (tryptic soy broth) at 20°C as a function of pH and NaCl concentrations, with gelatine concentrations of 0 and 50 g/l. Adapted from Theys et al. (2010).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 3: Growth/no growth regions of Salmonella Typhimurium in TSB (tryptic soy broth) at 20°C as a function of pH and NaCl concentrations, with gelatine concentrations of 0 and 50 g/l. Adapted from Theys et al. (2010).
Mentions: The growth of a strain of Salmonella enterica subsp. enterica serotype Typhimurium (named S. Typhimurium thereafter) in gelatine medium was compared to its growth in broth, at different conditions of pH and NaCl (Brocklehurst et al., 1995). The results show that S. Typhimurium behaves the same when growing in colonies and in a planktonic culture when under optimal conditions (pH = 7 and NaCl concentration of 0.5%). However, the generation time t (t = log2/μ where μ is the growth rate) was increased by a factor between 1.3 and 2 in the more stressful conditions (pH = 5 and NaCl concentration of 3.5%). The growth rates of this bacterial strain were thus ordered as follow: μplanktonic > μsubmerged > μsurface regardless of the aw when the NaCl concentration was 0.5%, and regardless of the NaCl concentration for maximum aw (Brocklehurst et al., 1997). The maximum viable cell counts were less affected by a low value of aw reduced by high sucrose and NaCl concentrations if the colony was submerged rather than on the surface. An explanation could be that the substrates are only accessible through the small area of the underside of surface colonies, whilst it is accessible all around the colony on a bigger area when submerged. By comparing a strain of S. Typhimurium growing as submerged colonies or in planktonic culture, it was shown that the aw was the most influential parameter on the growth rates (Theys et al., 2008). However, decreasing aw by increasing NaCl concentration was relatively more harmful to the growth of colonies, because of the combined effect on osmotic pressure, than by increasing gelatine concentrations of the media (Theys et al., 2010). In agreement with the latter, a lower growth rate of growth was observed in planktonic cultures than in submerged colonies of a strain of S. Typhimurium and the growth in colonies increased its sensitivity to the inhibition exerted by oregano oil (Skandamis et al., 2000). Surprisingly, the growth rate of submerged colonies of S. Typhimurium was found lower in broth than in agar medium, but lower in gelatine medium than in broth (Walker et al., 1998). Furthermore, when the growth rate was not affected by the immobilization of bacteria, the lag phase was increased in comparison to planktonic growth (Knudsen et al., 2012; Nielsen et al., 2013). Figure 3 is an example of the detrimental effect of immobilization of bacteria on their growth when under severe conditions such as low pH and high concentration of NaCl.

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