Abstract
Lactic acid bacteria (LAB) strains OB14 and OB15 were isolated from traditional Tunisian fermented dairy products, Testouri cheese and Rigouta, respectively. They were identified as Enterococcus faecalis by the MALDI TOF-MS (matrix assisted laser desorption-ionization time of flight mass spectrometry) biotyper system and molecular assays (species-specific PCR). These new isolates were evaluated for probiotic properties, compared to E. faecalis Symbioflor 1 clone DSM 16431, as reference. The bacteria were found to be tolerant to the harsh conditions of the gastrointestinal tract (acidity and bile salt). They were low to moderate biofilm producers, can adhere to Caco-2/TC7 intestinal cells and strengthen the intestinal barrier through the increase of the transepithelial electrical resistance (TER). Susceptibility to ampicillin, vancomycin, gentamicin and erythromycin has been tested using the broth microdilutions method. The results demonstrated that E. faecalis OB14 and OB15 were sensitive to the clinically important ampicillin (MIC = 1 μg/mL) and vancomycin (MIC = 2 μg/mL) antibiotics. However, Whole Genome Sequencing (WGS) showed the presence of tetracycline resistance and cytolysin genes in E. faecalis OB14, and this led to high mortality of Galleria Mellonella larvae in the virulence test. Hierarchical cluster analysis by MALDI TOF-MS biotyper showed that E. faecalis OB15 was closely related to the E. faecalis Symbioflor 1 probiotic strain than to OB14, and this has been confirmed by WGS using the average nucleotide identity (ANI) and Genome-to-Genome Hybridization similarity methods. According to these results, E. faecalis OB15 seems to be reliable for future development as probiotic, in food or feed industry.
Highlights
Enterococci are normal inhabitants of the gastrointestinal tract of humans and animals
The analysis by MALDI biotyper classified OB14 and OB15 isolates as E. faecalis strains with score value >2.0, which allows to identify at the species level with no doubt (Sogawa et al, 2011)
After the investigation of these beneficial attributes for E. faecalis OB14 and OB15 as probiotic candidates, we examined the safety of the bacteria using various tests
Summary
Enterococci are normal inhabitants of the gastrointestinal tract of humans and animals. These bacteria are ubiquitous in nature and have been used in the food industry as probiotics (Franz et al, 2003), or as starter culture in manufacturing cheese in high salt content and low pH (Wessels et al, 1991). They contribute to the characteristic taste of traditional Mediterranean cheeses and can be present in other fermented foods such as sausages, olives, and vegetables. Some enterococci strains produce simultaneously several bacteriocins, which give them a competitive advantage toward other microbes for colonization and niche control (Hanchi et al, 2018)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
