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The aim of this work was to study the biogenic amine content of brine-ripened cheeses after one year of storage and then to investigate possible contaminating micro-organisms with decarboxylase activity. The biogenic amine production of isolates was tested in vitro. The most frequent biogenic amines were putrescine, histamine and tyramine. The biogenic amine content detected in one cheese sample was above 120 mg/kg; this can be considered toxicologically relevant. Decarboxylase activity was found for 33 contaminating micro-organisms. Isolates belonging to Bacillus licheniformis, Debaryomyces hansenii, Staphylococcus equorum and Serratia marcescens produced significant amounts of putrescine and cadaverine.

Abstract:Složilová I., Purkrtová S., Kosová M., Mihulová M., Šviráková E., Demnerová K. (2014): Antilisterial activity of lactic acid bacteria against Listeria monocytogenes strains originating from different sources. Czech J. Food Sci., 32: 145-151.Eight individual bacteriocin-producing lactic acid bacteria (LAB) strains and three bacteriocin-non-producing cheese starter cultures were evaluated for their ability to inhibit the growth of six Listeria monocytogenes strains, originating from the guinea-pig lymph nodes, raw cow milk, and manufacturing dairy equipment. Results showed that either live cells or cell-free neutralised supernatant (CFNS) and/or heated CFNS of six individual LAB strains (Lcc. lactis subsp. lactis CCDM 416 and NIZO R5, Lbc. plantarum HV 11 and DC 1246, P. acidilactici HV 12, and Ent. mundtii CCM 1282) and one starter culture (DELVO-ADD ® 100-X DSF) were effective in the suppression of at least one listeria strain. Neither any individual LAB strain nor starter culture was antagonistic toward all studied L. monocytogenes strains, indicating diverse sensitivity/resistance among L. monocytogenes strains to antimicrobial compounds of LAB. The significant susceptibility of listerias isolated from raw milk and dairy equipment together with the strong antilisterial activity of DELVO-ADD ® 100-X DSF could be applied in dairy technology, where commonly used starter cultures could play both the biopreservative and fermentation role.

Although some metallic nanoparticles (NPs) are commonly used in the food processing plants as nanomaterials for food packaging, or as coatings on the food handling equipment, little is known about antimicrobial properties of palladium (PdNPs) and platinum (PtNPs) nanoparticles and their potential use in the food industry. In this study, common food-borne pathogens Salmonella enterica Infantis, Escherichia coli, Listeria monocytogenes and Staphylococcus aureus were tested. Both NPs reduced viable cells with the log10 CFU reduction of 0.3–2.4 (PdNPs) and 0.8–2.0 (PtNPs), average inhibitory rates of 55.2–99% for PdNPs and of 83.8–99% for PtNPs. However, both NPs seemed to be less effective for biofilm formation and its reduction. The most effective concentrations were evaluated to be 22.25–44.5 mg/L for PdNPs and 50.5–101 mg/L for PtNPs. Furthermore, the interactions of tested NPs with bacterial cell were visualized by transmission electron microscopy (TEM). TEM visualization confirmed that NPs entered bacteria and caused direct damage of the cell walls, which resulted in bacterial disruption. The in vitro cytotoxicity of individual NPs was determined in primary human renal tubular epithelial cells (HRTECs), human keratinocytes (HaCat), human dermal fibroblasts (HDFs), human epithelial kidney cells (HEK 293), and primary human coronary artery endothelial cells (HCAECs). Due to their antimicrobial properties on bacterial cells and no acute cytotoxicity, both types of NPs could potentially fight food-borne pathogens.

We determined the disinfectant effects of benzalkonium chloride (BC) and Savo (SV), a chlorine compound, on the biofilm and planktonic cells in 23 strains S. aureus mainly food isolates. The biofilm formation was performed in a model system using microtiter polystyrene plates COSTAR 3797 in trypton-soy broth with 1% glucose at 30°C. Benzalkonium chloride (BC) at 125 mg/l, applied directly on 24 h old biofilm, was able to remove the biofilm matrix in 21 strains, and to stop the reproduction of the biofilm cells in 23 strains. BC at the concentration of 125 mg/l was lethal to planktonic cells, coincubated for 24 h or treated for 10 minutes. None of the strains studied was able to grow in SV at 1X recommended concentration, while the safety lethal concentration for planktonic cells treated for 10 min was 4X. The application of 4X concentration SV into the 24 h old suspension removed the biofilm matrix in all strains and devitalised the biofilm cells in 10 strains and inhibited the viability in 13 strains by 70%.