Identification and characterization of Lactobacillus paracasei strain with probiotic properties isolated from faeces of healthy adult volunteers

Introduction: Lactobacillus spp. strains have been suggested to play an importarli role in thè formation and establishment of a well-bal- anced gut microbiota. The aim of thè present study was to isolate, identify and characterize novel Lactobacillus spp.strains with potential properties from thè faeces of healthy adult vol- unteers.Materials and Methods: A total of 18 healthy adult volunteers were selected and their fresh faecal samples were cultivated according to Munoz-Quezada et al. (2013). The isolates in pure culture on Rogosa medium were ana- lyzed by Grani stain and catalase test. Nine slrains Gram-positive with rod morphology and catalase-positive were screened for resis- tance to low pH and bile salts as described by Munoz-Quezada et al. (2013). The strain show- ing good resistance to gastrointestinal condi- tions was tested for adhesion properties using methods described by Guglielmetti et ai (2010) and Munoz-Quezada et al. (2013). The strain re- sistant to thè gastrointestinal conditions, and also exhibitingability to adhere to human in- lestìnal epithelial celi lines HT29 was idenlified by 16S rRNA gene sequencing as described by Yu et al. (2012). From purified extracted DNA thè 16S rRNA gene was amplified using prim- ers 16S-FA and 16S-RA described by Sun et al. (2010). The purified PCR fragments were used for sequencing by thè corresponding sequenc-ing primers.Furthermore, antibiotic susceptibility of thè strain was performed by determination of Min- inuim Inibitory Concentration (MIC) using thèmicrotiler broth dilution as suggested by Clini- cai and Labomtory Standards Institute (CLSI) 20 LO for Lactobacillus spp. and testing thè anti- biotics recommended by European Food Safety Authority (EFSA) 2012. Screening for antago- nistic activity of thè strain against Enterococ- CLLS faecalis ATCC 51299 and Escherìchia coli ATCC 43895 as described by VizosoFinto et al. (2006), was also performed.Results: The selected strain exhibited resis- tance to low pH, tolerance to high concentra- tions of bile salts, and a good in vitro adhesion to HT29 cells with both assays. The obtained sequences, approximately 1,400 bp, character- ized thè strain as L. paracaseì, showing nucleo- tide identity of 98.2%. The strain was suscep- tible to thè tested antibiotics, except to vanco- mycin. The novel strain showed antagonistic activity against E. faecalis ATCC 51299 and E. coli A TCC 43895.Discussion and Conclusioni Firstly in se- lecting potential probiotic strains, thè identi- fication at species level, and thè evaluation of physic-chemical and functional properties, of antagonistic activity and of thè antibioticsus- ceptibility, are highly important. Further re- searches will be performed to characterize our isolate at strain level, to evaluate possible toxi- cological activities and to test in vivo activity against different enteropathogens and immu- nomodulating properties.