Résumé:
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.
