Abstract
<p><strong>Objective: </strong>Investigate the influence of the antimicrobial peptides P34 and nisin on the expression of genes associated with components of the cell surface of <em>Listeria monocytogenes</em> and <em>Listeria seeligeri</em>.</p><p><strong>Methods: </strong>Antimicrobial activity was determined by addition of peptide P34 and nisin (12.5 µg/ml) onto Brain Heart Infusion agar (BHI) plates previously inoculated with indicator strains (<em>L. monocytogenes</em> ATCC 7644 or <em>L. seeligeri </em>AC 82/4) after incubation for 24 h at 37 °C or 240 h at 4 °C. Ribonucleic acid (RNA) was directly extracted from bacterial colonies at the border of the inhibition zones, and the expression levels of genes D-alanine-D-alanyl carrier protein ligase<em> (dltA), </em>putative phospholipid lysinylation<em> </em>(<em>Imo 1695</em>)<em> </em>and EIIAB<sup>Man</sup> of mannose-specific PTS<em> </em>(<em>mptA</em>) were determined using real-time PCR.</p><p><strong>Results</strong><strong>: </strong>A non-significant increase in the levels of transcription of genes <em>dltA, Imo1695 </em>and<em> mptA</em> was observed for <em>L. monocytogenes </em>treated with peptide P34 or nisin. Both peptides caused a similar decrease in <em>dltA</em> gene expression in <em>L. seeligeri</em>. The expression of gene <em>Imo1695</em> significantly decreased (about 2000-fold) after treatment with the peptide P34 at 37 °C, while at 4 °C a reduction of 12-fold and 5-fold was detected for P34 and nisin, respectively. A significant decrease in <em>mptA</em> gene expression was observed by exposition to peptide P34 (31.872-fold) and nisin (16.047-fold) for 24 h at 37 °C.</p><p><strong>Conclusion: </strong>The results suggest that both peptide P34 and nisin influence the expression of genes related with the cell-surface/cell-membrane structure of <em>L. seeligeri</em> and in lesser extent <em>L. monocytogenes</em>.</p>
Highlights
The genus Bacillus encompasses a number of industrially important species that have been recognised for years and are considered safe for biotechnological purposes
The inhibition zones of peptide P34 and nisin against L. monocytogenes and L. seeligeri after the incubation time of 24 h at 37 °C and 240 h at 4 °C are shown in table 1
This study showed that nisin produced larger inhibitory halos than the peptide P34 against the strain of L. seeligeri, both substances were inhibitory to the Listeria strains tested
Summary
The genus Bacillus encompasses a number of industrially important species that have been recognised for years and are considered safe for biotechnological purposes. Bacteriocins and bacteriocin-like substance (BLS) are antimicrobial peptides produced by diverse bacteria and are often effective against closely related species [4, 13]. BLS have gaining increased attention due to their potential use as natural preservatives in the food industry, due to activity against many pathogenic bacteria and the highest activity against Listeria species [14, 15]. An example is a nisin, a non-toxic bacteriocin hydrolyzed by digestive enzymes that have been used for over 50 y as a food preservative in different countries without the substantial development of bacterial resistance [16, 17]. It was believed that bacteria could not acquire resistance to antimicrobial peptides, so these substances would be strong candidates for new preservative in foods [18,19,20]. The development of resistance to antimicrobial peptides from previously sensitive strains has been viewed as difficult not impossible, but some studies have revealed that certain genes can provide increased resistance to antimicrobial peptides [21]
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