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Characterization of two safe <i>Enterococcus</i> strains producing enterocins isolated from Egyptian dairy products

El-Ghaish, S., Hadji-Sfaxi, I., Ahmadova, A., Choiset, Y., Rabesona, H., Sitohy, M., Haertlé, T., Chobert, J. -M.
Beneficial microbes 2011 v.2 no.1 pp. 15-27
Enterococcus faecium, Lactobacillus brevis, Lactobacillus delbrueckii subsp. bulgaricus, Listeria innocua, Listeria ivanovii, Listeria monocytogenes, antibacterial properties, bacteria, catalase, cell free system, chloramphenicol, chymotrypsin, dairy products, enterocins, gene amplification, heat, pH, polymerase chain reaction, ribosomal DNA, sodium chloride, structural genes, temperature, tetracycline, trypsin, virulence
<p>Five bacterial cocci isolates were selected from a wide pool of 503 isolates collected from traditional Egyptian dairy products on the basis of their inhibitory activities against <i>Lactobacillus brevis</i> F145, <i>Lactobacillus bulgaricus</i> 340, <i>Enterococcus faecium</i> HKLHS, <i>Listeria ivanovii</i> ATCC, <i>Listeria innocua</i> CIP 80.11 and <i>Listeria monocytogenes</i> EGDe 107776. These 5 isolates were identified as <i>E. faecium</i> TX1330 and <i>E. faecium</i> E980 by 16S rDNA amplification and sequencing. The antibacterial activity of the two strains was not affected by treatment of the cell free culture supernatant with catalase but their activities disappeared completely when digested with protease K, α-chymotrypsin and trypsin. The antimicrobial substance was stable over a wide range of pH (2-10) and was active after heating at 100 °C for 10 min. Bacteriocin yield in two strains reached a maximum (1,600 AU/ml) at the end of the exponential phase (6 h) and remained stable until the end of 24 h-incubation period when the medium reached pH 5.5. Maximal production of bacteriocin was obtained when growing the bacterial cells at temperatures ranging between 30 and 37 °C. Bacteriocin production was unaffected when the bacterial cells grew under severe conditions of pH (9.6) and in high salt (6.5% NaCl). Thanks to PCR gene amplification the bacteriocins produced by <i>E. faecium</i> TX1330 could be identified as enterocins A and B structural genes, while the bacteriocins produced by <i>E. faecium</i> E980 could be identified as enterocins P and L50A structural genes, which can be classified into two enterocin subclasses (IIa and IIc), respectively. PCR amplification demonstrated that the two studied strains did not contain virulence factors <i>asal, cyl</i> A and B, <i>ace, efaAfs</i> and <i>espfm</i>. These two strains were sensitive to most of the tested antibiotics but were resistant to tetracycline. <i>E. faecium</i> E980 was also resistant to chloramphenicol.</p>