Browsing by Autor "Lenz, Romina M"

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Application of spray-dried bacteriocins as cheese biopreservatives.
(2025) Lenz, Romina M; Guitián, M Virginia; Villalva, Fernando J; Goncalvez de Oliveira, Enzo; Soria, M Cecilia; Audisio, M Carina; Ibarguren, Carolina
Listeria monocytogenes can contaminate refrigerated ready-to-eat foods, such as cheeses. Enterocins, with a strong listericidal effect, constitute a natural alternative to control this pathogen in food. To optimize their antimicrobial action in food matrices, bacteriocins can be immobilised in edible coatings through spray drying technology which allows the large-scale production of microcapsules of bioactive molecules. The aim of this work was to evaluate the antimicrobial effectiveness of Enterococcus avium DSMZ17511 bacteriocins, obtained in a low-cost culture broth (HS-L), spray-dried assaying different thermoprotective materials (maltodextrin, cheese whey and brea gum), and incorporated into agar-based active coatings applied on goat cheese pieces artificially contaminated with L. monocytogenes 99/287. The bacteriocin solution (BS) powders, labelled HS-L BS, maintained the antimicrobial activity even after 90 days of storage, with titres up to 128,000 UA/g, with the least thermoprotective effect exerted by brea gum (64,000-32,000 UA/g). An increase in antimicrobial titre was observed for all bacteriocin powders after 3 months, despite storage conditions; probably due to a release effect from the encapsulated bacteriocin or a combined release and gradual dehydration effect of the encapsulating matrix. Also, the dried products stored at 25 °C hydrated easily, while refrigeration or freezing did not affect the powders texture. For coatings applied on fresh goat cheese, only a difference of 0.5 log cfu/mL was observed between the viability of L. monocytogenes in the contaminated active-coated cheese and the control without coating. Instead, for the commercial goat cheese, with a drier matrix, the viability values stood 1.0 log cfu/mL below the control uncoated cheeses for up to 10 days. These spray dried bacteriocin powders provide an alternative for their application as food biopreservatives, since stable dehydrated products were obtained, with prolonged antimicrobial activity, and with verified inhibitory action in a food matrix.
Response of sensitive and resistant Listeria monocytogenes strains against bacteriocins produced by different Enterococcus spp. strains.
(2022) Ibarguren, Carolina; Guitián, M Virginia; Lenz, Romina M; Cecilia, Soria M; Audisio, M Carina
Listeria monocytogenes is a relevant foodborne pathogen causing invasive listeriosis in humans, a disease with high mortality rates. Its ubiquity and growth characteristics enable this pathogen to survive harsh food processing environments. The addition of bacteriocins, antimicrobial peptides ribosomally synthesized by certain bacteria, appears as a natural alternative to control this pathogen in food. However, the emergence of L. monocytogenes strains resistant to the inhibitory action of bacteriocins has been detected. In order to analyse the development of this resistance, different properties of L. monocytogenes strains susceptible to bacteriocins (strains 01/155, 99/287 and 99/267) and their respective resistant isolates (strains 01/155B6R, 99/287B6R, 99/286C1R, 99/287 Mo1R, 99/287 M1bR, 99/287 M2dR, 99/267B6R), were compared in this work. Differences were analysed in: a) growth of the pathogen strains in direct contact with bacteriocin solution, in co-cultures with the producing strain, or with different sugars; b) response to antibiotics typically used against listeriosis; c) changes in cell morphology, observed by transmission or scanning electron microscopy; d) expression of mobility and haemolysin activity, two of L. monocytogenes main virulence factors; and e) biofilm formation ability. For all the isolates, the acquired resistance was permanent and crossed between the different bacteriocins under study. An inhibitory effect was observed for resistant strains only when they were grown in mixed culture with any of the bacteriocin-producing strains, with an acidified medium as additional growth stress. In all cases, the decrease in viability was lower for resistant strains and followed a particular profile for each strain. The variation of sugar substrate influenced resistant variants growth ability, with a more pronounced difference in the medium supplemented with glucose. Susceptibility to antibiotics was similar or higher for resistant variants, while neither the mobility nor the haemolytic activity presented differences among resistant or susceptible strains. Finally, the resistant variants showed a greater capacity to form biofilms, although this effect was reversed when grown in the presence of bacteriocins. Each resistant isolate had a particular behaviour pattern, and the acquisition of resistance appeared to be strain and bacteriocin dependent. These results contribute to the knowledge of L. monocytogenes bacteriocin-resistance development, which is essential to favour the use of these peptides as biopreservatives.