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Summary
The objective of this work is to demonstrate the probiotic potential of 13 different Gramnegative bacterial strains isolated from the digestive tract of the mollusk Sepia officinalis for
possible applications in aquaculture. The 13 strains were first identified and tested for: their
antimicrobial activity against 5 pathogenic indicator strains (Pseudomonas aeruginosa,
multiresistant E.coli ECTC8, E.coli k12, Aeromonas hydrophila and Vibrio fluvialis), their
antibiotic resistance and their biofilm production. The results obtained led to the selection of 3
strains of Pseudomonas aeruginosa considered to be of interest (Pseudo1, Pseudo2 and
MK7). The 3 strains exhibited significant antimicrobial activity against 4 indicator strains
(except for Pseudomonas aeruginosa). The Pseudo1 and MK7 strains are average producers
of biofilm and the Pseudo2 strain is a strong producer of biofilm. The 3 strains exhibited a
profile of natural resistance to different antibiotics and sensitivity to Aztreonam, Amikacin,
Gentamicin and Ciprofloxacin in addition to Cefoxitin for the Pseudo2 strain. Secondly, the 3
strains were tested for their resistance to gastric pH and bile salts as well as for their
hemolytic activity. All 3 strains are resistant to acidic pH and bile salts. The pseudo2 and
MK7 strains exhibited partial hemolysis (a-hemolysis) and only the Pseudo1 strain didn’t
exhibit a hemolytic activity. The results obtained show that the 3 strains meet the functional
and the safety criteria. They represent promising probiotic candidates in the field of
aquaculture especially that Pseudomonas aeruginosa has already proven its effectiveness as a
probiotic in the treatment of water and in the improvement of the health status of aquatic
species of breeding.
Key words: probiotics, Sepia officinalis, antimicrobial activity, Pseudomonas aeruginosa,
biofilm production, aquaculture.
Summary
The objective of this work is to demonstrate the probiotic potential of 13 different Gramnegative bacterial strains isolated from the digestive tract of the mollusk Sepia officinalis for
possible applications in aquaculture. The 13 strains were first identified and tested for: their
antimicrobial activity against 5 pathogenic indicator strains (Pseudomonas aeruginosa,
multiresistant E.coli ECTC8, E.coli k12, Aeromonas hydrophila and Vibrio fluvialis), their
antibiotic resistance and their biofilm production. The results obtained led to the selection of 3
strains of Pseudomonas aeruginosa considered to be of interest (Pseudo1, Pseudo2 and
MK7). The 3 strains exhibited significant antimicrobial activity against 4 indicator strains
(except for Pseudomonas aeruginosa). The Pseudo1 and MK7 strains are average producers
of biofilm and the Pseudo2 strain is a strong producer of biofilm. The 3 strains exhibited a
profile of natural resistance to different antibiotics and sensitivity to Aztreonam, Amikacin,
Gentamicin and Ciprofloxacin in addition to Cefoxitin for the Pseudo2 strain. Secondly, the 3
strains were tested for their resistance to gastric pH and bile salts as well as for their
hemolytic activity. All 3 strains are resistant to acidic pH and bile salts. The pseudo2 and
MK7 strains exhibited partial hemolysis (a-hemolysis) and only the Pseudo1 strain didn’t
exhibit a hemolytic activity. The results obtained show that the 3 strains meet the functional
and the safety criteria. They represent promising probiotic candidates in the field of
aquaculture especially that Pseudomonas aeruginosa has already proven its effectiveness as a
probiotic in the treatment of water and in the improvement of the health status of aquatic
species of breeding.
Key words: probiotics, Sepia officinalis, antimicrobial activity, Pseudomonas aeruginosa,
biofilm production, aquaculture.