29G-24 |
Sub-lethal stress and protein profile changes in Listeria monocytogenes |
S. TIPPARAJU1, N. Maks, P. J. Slade1, and S. Ravishankar1. (1) National Center for Food Safety & Technology, Illinois Institute of Technology, IIT Moffett Campus, 6502 S.Archer Rd., Summit-Argo, IL 60501
Several minimal physical and chemical treatments used to
preserve foods result in incomplete inactivation of microorganisms when
inadequate, resulting in generation of sub-lethally injured cells. Very little
is known about the adaptive changes occurring in L. monocytogenes under
such conditions, and how this relates to pathogenicity of the species. Our objective was to determine the exact sub-lethal values
of acidic pH, low aw and high temperature causing stress during
minimal processing conditions, and to analyze protein profiles generated under
stress and to compare profiles between different lineages of L. monocytogenes. L. monocytogenes strains [CFSAN 213 & 219
(Lineage I), 221 & 223 (Lineage II), 228 & 229 (Lineage III)] were
tested. Tryptic soy broth without dextrose (TSB w/o D) was the suspending
medium. The strains were evaluated at acidic pH (3.5 - 5.0), aw
levels (0.84 – 0.96) and temperatures (43 – 46 oC). Plus or minus
one log change in the initial population (106 – 107 log
cfu/ml) after 24 hours was considered to represent the sub-lethal condition in
each case. Bacteria were sub-lethally stressed for 1 h and centrifuged. Pellets
were re-suspended in extraction buffer and sonicated to extract protein.
Two-dimensional PAGE was performed using the extracted protein. Gels were
analyzed using Phoretix 2D advanced gel software. Sub-lethal aw for all the lineages was 0.84.
Sub-lethal pH value for lineages III and I was 4.0 and for lineage II 4.5.
Sub-lethal temperature for lineages II and I was 44 oC and for
lineage III 45 oC. Changes in the protein profile of strains between
lineages were more noticeable than those of strains within the same lineage. This study will improve understanding of the relationship between stress adaptation and phylogenetic lineage. This will improve the ability to evaluate the significance of the presence of particular strains in foods processed under certain conditions.
Session 29G, Food Microbiology: General
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