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See detailIdentification et caractérisation de bactériocines produites par deux bactéries lactiques (Enterococcus faecium CWBI-B1430 et Enterococcus mundtii CWBI-B1431) isolées à partir de fromages frais artisanaux péruviens
Aguilar Galvez, Ana Consuelo ULg

Doctoral thesis (2011)

A screening of lactic acid bacteria (LAB) with bacteriocin-like inhibitory activity against Listeria monocytogenes was performed. The screening was conducted in 27 traditional artisanal-produced cheeses ... [more ▼]

A screening of lactic acid bacteria (LAB) with bacteriocin-like inhibitory activity against Listeria monocytogenes was performed. The screening was conducted in 27 traditional artisanal-produced cheeses obtained from different Peruvian regions. Two thousand two hundred and seventy seven strains (2277) were isolated, of which 20 exhibited bacteriocin-like inhibitory activity, two strains stand out for having higher activity against listeria, as well as stability at pH value of 2-11 and a thermal stability. The two strains were identified using 16 S ribosomal DNA method, and were registered in the GenBank database of NCBI (National Center for Biotechnology Information). These were Enterococcus faecium CWBI-B1430 (accession number EF591817) and Enterococcus mundtii CWBI-B1431 (accession number EF591816). Two of the major factors concerned in a potential health risk associated with the genus Enterococcus were evaluated, and it was demonstrated that they were sensitive to vancomycin and showed no hemolytic activity. Genetic studies showed the presence of four putative bacteriocin genes in both strains, these were enterocin A, enterocin B, enterocin P, and mundticin KS. The reverse transcription-PCR analysis was realized, the expression of the bacteriocin genes enterocin A, enterocin B, and mundticin KS in CWBI-B1430 was showed, while bacteriocin genes enterocin P and mundticin KS was demonstrated in CWBI-B1431. These results are the first report of the expression of mundticin KS in E. faecium and enterocin P in E. mundtii. Also, the expression was studied at different temperatures, unlike the enterocin P, where only a positive signal was obtained at 12 and 37°C. All other enterocin showed positive signal at 12, 30, 37 and 42°C. The production of bacteriocins on a small scale, in both strains was studied. It was investigate the influence of initial pH (4.5, 5.0, 5.5, 6.0, 6.5 and 7.0), temperature (25, 30 and 37°C) and oxygen level (anaerobic, microaerobic and aerobic). The conditions for maximizing the production of bacteriocins are : initial pH of 7.0, at 37 °C, and microaerobic conditions for CWBI-B1430 strain; initial pH of 6.5, at 37 °C, and an aerobic condition for CWBI-B1431. The influence of the source of carbon and nitrogen, as well as their concentration in the bacteriocin production, was studied. The study of the production of short-chain fatty acids by these strains of multiproducing bacteriocins, showed the propionic acid as the most important. The purification study confirmed that the two bacteria in question are multi-producing of bacteriocins, as shown by the obtained chromatograms, showing different molecular weights, different charge and hydrophobicity level. The results of in situ application of the two selected strains or their supernatant does not show the same efficiency as those obtained in vitro. Factors such as temperature and food composition may be the origin of these results. Therefore, we propose the use of both strains in the food industry, for being multi-producing bacteriocins, have broad spectrum of inhibition and because the substances that produce have functional properties that are useful in the food industry. [less ▲]

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See detailThe influence of growth conditions on enterocin-like production by Enterococcus faecium CWBI-B1430 and Enterococcus mundtii CWBI-B1431 isolates from artisanal Peruvian cheeses
Aguilar Galvez, Ana Consuelo ULg; Guillermo Arciniegas, Sandra Denisse; Dubois Dauphin, Robin ULg et al

in Annals of Microbiology (2011), 61

Strains of Enterococcus faecium CWBI-B1430 and Enterococcus mundtii CWBI-B1431, isolated from artisanal-produced Peruvian cheeses, offer a broad potential application as food biopreservatives for heat ... [more ▼]

Strains of Enterococcus faecium CWBI-B1430 and Enterococcus mundtii CWBI-B1431, isolated from artisanal-produced Peruvian cheeses, offer a broad potential application as food biopreservatives for heat-processing treatments. The aim of this work was to optimize the production conditions and medium composition for the production of bacteriocin-like substances (BLIS). The kinetics of the BLIS production for both strains is a growth-associated process, and the maximum inhibitory activity for E. faecium CWBI-B1430 and E. mundtii CWBI-B1431 was achieved after 9 and 8 h of fermentation, respectively. Temperature, initial pH, oxygen level, and their interactions all influence BLIS production for both strains; this influence was specific for each strain. The bacteriocin gene expression in a 20.0-L fermentor confirms previous work carried out by fermentation in the flask; the first reports of expression revealed mundticin KS from E. faecium and enterocin P from E. mundtii. Both strains demonstrated antilisteria activity and were multi-producers of enterocin. Furthermore, the study with whey milk as an inexpensive source of fermentable carbohydrates indicated lower BLIS production than that obtained with M17LG broth. The short chain fatty acid (SCFA) analyses offer a new alternative use for both strains, as strains probiotic, for propionic acid production. [less ▲]

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See detailDescription of two Enterococcus strains isolated from traditional Peruvian artisanal-produced cheeses with a bacteriocin-like inhibitory activity
Aguilar Galvez, Ana Consuelo ULg; Dubois Dauphin, Robin ULg; Ghalfi, Hakim et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2009), 13(3), 349-356

The aim of this work was to isolate and to characterize strains of lactic acid bacteria (LAB) with bacteriocin-like inhibitory activity from 27 traditional cheeses artisanal-produced obtained from ... [more ▼]

The aim of this work was to isolate and to characterize strains of lactic acid bacteria (LAB) with bacteriocin-like inhibitory activity from 27 traditional cheeses artisanal-produced obtained from different Peruvian regions. Twenty Gram+ and catalasenegative strains among 2,277 isolates exhibited bacteriocin-like inhibitory activity against Listeria monocytogenes CWBIB2232 as target strain. No change in inhibitory activity was observed after organic acid neutralization and treatment with catalase of the cell-free supernatant (CFS). The proteinic nature of the antimicrobial activity was confirmed for the twenty LAB strains by proteolytic digestion of the CFS. Two strains, CWBI-B1431 and CWBI-B1430, with the best antimicrobial activity were selected for further researches. These strains were taxonomically identified by phenotypic and genotypic analyses as Enterococcus mundtii (CWBI-B1431) and Enterococcus faecium (CWBI-B1430). The two strains were sensitive to vancomycin (MIC < 2 μg.ml-1) and showed absence of haemolysis. [less ▲]

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