Bacteriocin production and safety evaluation of non-starter Enterococcus faecium IM1 and Enterococcus hirae IM1 strains isolated from homemade Egyptian dairy products

International audienceThis study presents the characterization of some strains of lactic acid bacteria (LAB) from traditional Egyptian dairy products. Isolated L(623 isolates) were studied for their antimicrobial activity against taxonomically related microorganisms. Selected Lwere identified by PCR method as Enterococcus faecium IM1 and Enterococcus hirae IM1. Partially purified enterocins showed antimicrobial activity against Lactobacillus bulgaricus 340, Lb. brevis F104 and F145, Lb. sakei, Brochothrix thermosphacta DSMZ20171(T) and DSMZ20599, Carnobacterium maltaromaticum CIP103135(T), C. piscicola S4312, E. faecalis JH2-2 and JH2-2rr04, E. faecium CTC492/t1362 and P13, Listeria grayi CLIP12518, L. innocua 1, CIP80.11(T), F and P, L. ivanovii ATCC and CIP78.42T, L. monocytogenes CIP78.35, DSM12464, EGDe, RF124, RF125, RF131, RF132, RF133, RF142, RF151 and RF152, and Vagococcus penaei CIP 109914(T) but have no effect against Bacillus subtilis 168T, Moellerella wisconsensis MIP2451, Morganella psychrotolerans MIP2488, Pseudomonas fluorescens 10, Salmonella enterica, Sal. montevideo, Sal. typhimurium and Serratia liquefaciens CIP103238(T). The inhibitory activity was not due to hydrogen peroxide for E. hirae IM1, but strain E. faecium IM1 may excrete diverse antimicrobial compounds such as hydrogen peroxide and bacteriocins. Antimicrobial activity of E. faecium IM1 was initially detected during exponential phase of growth, and the maximal level (1,300 AU/mL) was observed at 12 h and remained stable till the end of incubation time (48 h). Maximum of activity of E. hirae IM1 was observed during the logarithmic phase (6 h) and then decreased after 12 h. Bacteriocins produced by E. faecium IM1 and E. hirae IM1 were stable between pH 5 and pH 8 and stable also until 100 A degrees C/20 min. Tested strains were free from virulence determinant genes as well as hemolytic and gelatinase activities. E. faecium IM1 was sensitive to penicillin, kanamycin, vancomycin, gentamicin and tetracycline but resistant to ampicillin. Otherwise, E. hirae IM1 was sensitive to penicillin, kanamycin, vancomycin and tetracycline but resistant to ampicillin and gentamicin. The isolated cultures with antimicrobial activities may be used as safe and useful starter cultures or co-cultures

Bacteriocin-producing <em>Enterococcus faecalis</em> KT2W2G isolated from mangrove forests in southern Thailand: Purification, characterization and safety evaluation

International audienceThe aim of this work was to purify and characterize the bacteriocin produced by Enterococcus faecalis KT2W2G isolated from the mangrove forest in southern Thailand, in order to evaluate its potential as a new food protective agent. The active peptide from the cell-free supernatant of Ent. faecalis KT2W2G was purified in 4 steps: (i) precipitation with 70% saturated ammonium sulfate, (ii) elution on a reversed phase cartridge (Sep-Pak C8) using different concentrations of acetonitrile, (iii) cation-exchange chromatography and (iv) final purification by reversed phase-HPLC on a C8 column. Each purification step increased the specific activity and reduced the amount of contaminating non-bacteriocin proteins. The specific activity of purified bacteriocin was 13,470.53 AU/mg of protein, which corresponded to a 48.10- fold increase. TricineeSDS-PAGE of the purified bacteriocin gave molecular weight ranging between 3.5 and 6.5 kDa. The activity of the partially purified bacteriocin was unaffected by pH (2.0e12.0) and thermostable, but was sensitive to proteolytic enzymes. This bacteriocin maintained full stability after storage at 20, 4 and 37 C for 2 months. It was stable when incubated for 1 month at 4 C in 0e30% NaCl. Inhibitory spectrum of this bacteriocin showed a wide range of activities against other LAB, foodspoilage and food-borne pathogens. Ent. faecalis KT2W2G was sensitive to kanamycin, tetracycline and vancomycin but resistant to ampicillin, gentamicin and penicillin. PCR amplification demonstrated that Ent. faecalis KT2W2G does not harbor virulence genes cylA, cylB and esp but has virulence genes ace, asa1and efaAfs. The bacteriocin and its producing strain may find application as bio-preservatives for reduction of food-spoilage and food-borne pathogens in food products