Molecular characterization of a gene that is associated with Listeria monocytogenes serotype 4b-specific surface antigen expression

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Title: Molecular characterization of a gene that is associated with Listeria monocytogenes serotype 4b-specific surface antigen expression
Author: Li, Jianying
Advisors: Dr. Sophia Kathariou, Chair
Dr. Todd Klaenhammer, Member
Dr. Fred Breidt, Member
Abstract: Listeria monocytogenes is the cause of human listeriosis, a food borne disease with high mortality. Serotypes 1/2a, 1/2b, and 4b account for most cause of illness. Serotype 4b is of special interest, for its high implication in foodborne outbreaks. Two loci were previously found to be involved in serotype-specific surface antigen expression of L. monocytogenes serotype 4b. One mutant, 27B6, derived from L.monocytogenes serotype 4b strain 2381L (Jalisco cheese outbreak), was found to be negative in immunoblot reactions with all three serotype 4b-specific MAbs C74.22, C74.33, and C74.180. Chromatographic analysis showed markedly reduced levels of two sugar substituents on the teichoic acid backbone, compared with the wild type strain. The mutant was furthermore resistant to Listeria species-specific phage A511, while still sensitive to serotype 4b-specific phage 2671. In this study, the transposon localized in a new genomic region (locus III). The genes in this region had homologues in the database involved in galactose metabolism, including galM, galE, and pgm. The transposon in 27B6 was found to be in the putative pgm. Interestingly, although inactivation of the putative pgm affected the presentation of both serotype-specific sugar substituents on the teichoic acid, the gene was not found to be unique to serotype 4b. The gene pgm was present in L.monocytogenes serotypes other than 4b, while it was absent or highly divergent in other species. An in-frame deletion of pgm was constructed, showing similar phenotypes as those of the initial transposon mutant 27B6. The wild type pgm sequence could successfully complement mutant 27B6 in-trans, restoring wild-type reactivity with MAbs, as well as phage A511 sensitivity. In conclusion, this newly characterized genomic region of L.monocytogenes may function in sugar metabolism and is possibly associated with cell wall teichoic acid glycosylation in serotype 4b, being required for expression of serotype 4b-specific antigenic determinants as well as receptors for phage A511.
Date: 2001-07-11
Degree: MS
Discipline: Food Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/2853


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