PARTNER FEATURE ▶▶▶
Biofilms: the bacterial fortress
One common survival strategy used by bacteria is to form biofilms. These communities and their inherent resistance to antimicrobial agents are at the root of recurrent bacterial infections in livestock rearing.
BY FRANCK FOULON, GLOBAL PRODUCT MANAGER HYGIENE, HUVEPHARMA B
acteria have adapted to a “biofilmed” state to sur- vive unfavourable environmental conditions such as those which are poorly oxygenated, have extremes in temperature or are lacking in nutrients. In the
natural environment, biofilms act as a reservoir for microbial species, constitute a major component of the bacterial bio- mass and guarantee ecological balance. But in livestock buildings, they are a source of permanent contamination that is particularly difficult to eliminate. A livestock rearing house is a closed space with a dynamic mi- crobial ecosystem due to the high concentrations of organic matter, high temperatures and high humidity levels. The characteristics of this microbial ecosystem are determined by the microbiota of each animal and that of the herd. Animal excrement regularly enriches the microbiota of the building, especially with strains of enterococcus, coliforms,
lactobacillus and bacillus, which are all found in the digestive tract of the animals. The presence of animals in the barn caus- es an increase in the temperature and humidity of the ambi- ent air. This warm air rises to the top of the building, carrying with it many micro-organisms in the form of bioaerosols. Thus, all surfaces of the building become contaminated and biofilms are formed. Biofilms are complex structures, constituting a considerable bacterial reserve in livestock buildings. They are formed on surfaces through the accumulation of stacked bacteria which secrete a protective polysaccharide or extracellular polymeric substances (EPS) during the maturation phase. This mucous matrix is excreted through a network of channels in which the medium can circulate. The thickness of the biofilm does not increase indefinitely. Large aggregates or single cells may detach from mature bio- film and can directly seed other surfaces. The detachment of parts of the biofilm is partly due to variations in temperature and humidity inside the buildings. This contributes to air- borne bacterial spread, causing increased infectious pressure and new animal contaminations (see Figure 1). The structures forming biofilms contain channels in which nutrients can circulate, and cells in different regions of a biofilm exhibit different gene expressions. The biofilm is
Figure 1 - Steps leading to bacterial biofilm formation. Shear force Planktonic bacteria
Secondary bacterial species
Microcolony Surface
Proliferation
Growth/Maturation
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▶ PIG PROGRESS | Volume 37, No. 3, 2021
Reversible attachment
Detachment and reversion to planktonic growth
Biofilm collapse and cells release
Irreversible
attachment and cell-cell adhesion
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