Isolation, Molecular Detection and Antibiotic Activity of Streptococcus thermophilus isolates from Locally Fermented Milk Collected from Liben Chukala District, Oromia, Ethiopia

Abstract

Streptococcus thermophilus is one of the most economically important Lactic Acid Bacteria (LAB) with annual market value of 40 billion USD, and milk acidification makes it the of major technologically important in industrial fermentation processes. The purpose of this study was to isolate, detect by molecular tool and test it’s antibiotic activity of Streptococcus thermophilus from fermented milk samples originated from Liben Chukala District Oromia Regional State, Ethiopia. Isolation of S. thermophilus was carried out on M948 agar and characterized by biochemical tests. In the same way molecular detection of representative isolates of S. thermophilus was carried out by using two sets of primers (PA/pH and ThI/ThII) with their expected PCR product size of 1600 bp and 250 bp, respectively. This study showed that, molecular detection was more efficient than other biochemical tests for separation of S. thermophilus from other LAB. Moreover, an antibiotic activity test results revealed that S. thermophilus had the highest antibacterial activities against pathogenic Staphylococcus aurues than Clostridium difficile and E. coli with its highest zone of inhibition of 9.7±0.20 mm for S. aurues, 9.0±0.12 for Clostridium spp as well as 5.7±0.42mm for E. coli. This result implies that, gram positive S. thermophilus can inhibit other gram positive pathogens than gram negative bacterial species. On the other hand this study revealed that, the antibiotic activity test of S. thermophilus was more efficient in cellular suspension than in chemical extracts. This antibiotic activity against food borne pathogens enabled S. thermophilus to be used as biopreservatives in dairy industry. Accordingly this probiotic microorganism can be used in other industrial area to produce biosurfactants, bacteriocine, biotherapeutic, antibiotic and recombinant vaccine production due to its antibacterial activity.