Contribution à l’étude de la formation de biofilm par des souches industrielles de Streptococcus thermophilus

Abstract

The present work describes an experimental protocol aimed at demonstrating the formation of biofilm in industrial strains of Streptococcus thermophilus isolated from yoghurt and cheese, making the link with the biosynthesis of exopolysaccharides and highlighting certain molecular actors involved in this process. . At first, 20 industrial S. thermophilus strains from dairy products (i.e. yoghurt and cheese) were isolated and purified. All isolates were identified according to key microbiological and biochemical criteria (Gram stain, catalase test, 6.5% growth of NaCl (P/V), Sherman milk, and sugar fermentation and hydrolysis esculin). The evaluation step The formation of the biofilm by three different methods (polystyrene microplate (TCP), tube method (TM)) to detect the adhesion of S. thermophilus to two surfaces of different nature (polystyrene and glass ), so we adapted the method RCA (Red Congo agar) aims to confirm the production of slime under the same growing conditions. Knowing that the formation of biofilm involves some molecular actors (EPS and capsular EPS), the initial attachment that EPS intervenes is for this reason we sought the production of EPS by a simple visual detection and agar RRM17 (ruthenium red agar) under the same conditions described above, this work was finalized by highlighting the capsule with Indian ink. We found that all the strains are biofilm formers by the TCP and TM method with some difference of which one proportion is a strong trainer and the other alternates between moderate and weak. At the same time some strains showed slime production (strains with a dry black appearance). Knowing that this production varies quantitatively from one strain to another, this is related to the appearance of colony on RCA agar and the interpretation is thus relative to the references consulted. Regarding EPS biosynthesis is also the majority of strains are high producers and the rest is moderate, we have cleared the capsule in our strains of which they all form capsules.