Nanocomposite of Ag-Doped ZnO and AgO Nanocrystals as a Preventive Measure to Control Biofilm Formation in Eggshell and Salmonella spp. Entry Into Eggs.

Salmonella spp. is an important foodborne agent of salmonellosis, whose sources in humans often include products of avian origin. The control of this bacterium is difficult especially when Salmonella spp. is organized into biofilms. We hypothesized that the novel nanocomposites of ZnO nanocrystals doped with silver (Ag) and silver oxide (AgO) nanocrystals (ZnO:Ag-AgO) synthesized by the coprecipitation method could control or prevent the formation of Salmonella Enteritidis (SE) and Salmonella Heidelberg (SH) biofilm and its entry into turkey eggs. The diffraction characteristics of ZnO and AgO showed sizes of 28 and 30 nm, respectively. The Zn to Ag substitution into the ZnO crystalline structure was evidenced by the ionic radius of Ag+2 (1.26 Å), which is greater than Zn+2 (0.74 Å). For the SE analyses post-biofilm formation, the ZnO:Ag-AgO was not able to eliminate the biofilm, but the bacterial load was lower than that of the control group. Additionally, SE was able to infiltrate into the eggs and was found in both albumen and yolk. For the SH analyses applied onto the eggshells before biofilm formation, the ZnO:Ag-AgO treatment prevented biofilm formation, and although the bacterium infiltration into the eggs was observed in all treated groups, it was significantly smaller in ZnO:Ag-AgO pre-treated eggs, and SH could not reach the yolk. There was no difference in pore size between groups; therefore, the inhibition of biofilm formation and the prevention of bacterium entry into the egg were attributable to the use of ZnO:Ag-AgO, which was not influenced by the egg structure. Although the amount of Ag and Zn in the shell of the ZnO:Ag-AgO group was greater in relation to the control, this difference was not detected in the other egg components. In the search for new measures that are effective, safe and viable for controlling microorganisms in poultry farming, the application of a nanocomposite of Ag-doped ZnO and AgO nanocrystals appears as an alternative of great potential to prevent Salmonella sp biofilms in eggshells and other surfaces.

Probiotic properties of lactic acid bacteria isolated from water-buffalo mozzarella cheese.

This study evaluated the probiotic properties (stability at different pH values and bile salt concentration, auto-aggregation and co-aggregation, survival in the presence of antibiotics and commercial drugs, study of ß-galactosidase production, evaluation of the presence of genes encoding MapA and Mub adhesion proteins and EF-Tu elongation factor, and the presence of genes encoding virulence factor) of four LAB strains (Lactobacillus casei SJRP35, Leuconostoc citreum SJRP44, Lactobacillus delbrueckii subsp. bulgaricus SJRP57 and Leuconostoc mesenteroides subsp. mesenteroides SJRP58) which produced antimicrobial substances (antimicrobial peptides). The strains survived the simulated GIT modeled in MRS broth, whole and skim milk. In addition, auto-aggregation and the cell surface hydrophobicity of all strains were high, and various degrees of co-aggregation were observed with indicator strains. All strains presented low resistance to several antibiotics and survived in the presence of commercial drugs. Only the strain SJRP44 did not produce the ß-galactosidase enzyme. Moreover, the strain SJRP57 did not show the presence of any genes encoding virulence factors; however, the strain SJRP35 presented vancomycin resistance and adhesion of collagen genes, the strain SJRP44 harbored the ornithine decarboxylase gene and the strain SJRP58 generated positive results for aggregation substance and histidine decarboxylase genes. In conclusion, the strain SJRP57 was considered the best candidate as probiotic cultures for further in vivo studies and functional food products development.

Leuconostoc mesenteroides SJRP55: A Bacteriocinogenic Strain Isolated from Brazilian Water Buffalo Mozzarella Cheese.

The production of bacteriocins by Leuconostoc mesenteroides represents an important opportunity for exploration of their potential use for industrial purpose. The antimicrobial compounds produced by L. mesenteroides subsp. mesenteroides SJRP55 strain were characterized and purified. Cell-free supernatant of Leuc. mesenteroides subsp. mesenteroides SJRP55 produced antibacterial compounds against Listeria spp. strains and not inhibiting against Lactobacillus spp. The antimicrobial substances were stable at high temperatures (100 °C for 2 h and 121 °C for 20 min) and low pH (pH 2-4) values, but sensitive to proteolytic enzymes and resistant to α-amylase, lipase and catalase enzymes. The optimal temperature for active peptides production was 25 °C. The antimicrobial compounds were purified by ammonium sulfate precipitation, affinity column and reverse-phase chromatography. Mass spectrometry and amino acids analyses showed that the bacteriocins were identical to mesentericin Y105 and B105. The producer strain's DNA analysis revealed presence of open reading frames possibly coding for virulence factors, such as enterococcal surface protein (esp), collagen adhesion (ace) and intrinsic vancomycin resistance (vanA); however, biogenic amines encoding genes were not observed. Leuc. mesenteroides subsp. mesenteroides SJRP55 is a promising biopreservative culture in fermented milk, and the purified bacteriocins can also be applied in food preservation.