CELLS BY THE EFEECT OF LACTOCIN AL705 AND HIGH HYDROSTATIC PRESSURE ULTRASTRUCTURAL CHANGES OF LISTERIA

DALLAGNOL, A.M. ; BARRIO, Y.X.; VAUDAGNA, S.R.; CAP, M.; VIGNOLO, G.

Tucuman

Simposio; V International Symposium on Lactic Acid Bacteria (SIBAL). Benefitting from lactic Acid Bacteria. Progress in Health and Food.; 2016

CERELA-CONICET

Listeria (L.) monocytogenes is a foodborne pathogen which has been associated with the consumption of ready-to-eat (RTE) foods. To ensure safety of these products, new post-packaging food preservation strategies have been developed and applied in combination with antimicrobial additives. High hydrostatic pressure (HHP) and biopreservation are two new technologies that can be used as a combined strategy. HHP above 200 MPa is a post-packaging treatment for cold pasteurization due to its ability to kill and injure microbial cells. Bacteriocins are natural antimicrobial peptides produced by lactic acid bacteria that have inhibitory effect on Gram positive bacteria. The aim of this work was to evaluate the effect of HHP and lactocin AL705, an anti-listeria bacteriocin produced by Lactobacillus curvatus CRL705, on Listeria cells by transmission electron microscopy (TEM). A suspension (109 CFU/mL) from overnight culture of L. innocua 7 was prepared in PBS. The suspension was distributed (40 mL) in sterile plastic bags, with or without the addition 105 UA/mL of lactocin AL705, vacuum-packaged and/or pressurized at 400 MPa. After 2 h at 4 °C, viability of L. innocua was tested in TSB-YE agar and ultrastructural changes evaluated by TEM. Results showed similar counts (ca. 2x109 CFU/mL) for untreated samples and those added with lactocin AL705. However, HHP reduced Listeria population by one log (ca. 2x108 CFU/mL), whereas cells treated with the combination of lactocin AL705 + 400 MPa showed a 5 log-reduction reaching final cell counts of 4x104 CFU/mL. TEM studies showed that cells exposed to lactocin AL705 had an electron-transparent layer between the plasmatic membrane (PM) and the outer cell wall layer. Moreover, chromatin condensation and mesosome-like membranous formations were observed indicating severe injure on PM and pore formation. When L. innocua 7 was subjected to 400 MPa, protein condensation and higher separation between cell wall and PM were observed. When the combined effect of lactocin AL705 and HHP was evaluated, more marked ultrastructural cells damage was produced involving thickened or disrupted cell walls, cytoplasmic material protruding from the cell, waviness of the plasmatic membrane as well as cytoplasm-lacking cells. These results indicate that a combination of high pressure and lactocin AL705 may be suitable for improving the quality of minimally processed foods at lower hydrostatic pressure levels.