A Novel Serotype-Specific Gene Cassette ( gltA-gltB ) Is Required for Expression of Teichoic Acid-Associated Surface Antigens in Listeria monocytogenes of Serotype 4b

Abstract

Listeria monocytogenes serotype 4b strains account for about 40% of sporadic cases and many epidemics of listeriosis. Mutations in a chromosomal locus resulted in loss of reactivity with all three monoclonal antibodies (MAbs) which were specific to serotype 4b and the closely related serotypes 4d and 4e. Here we show that this locus contains a serotype 4b-4d-4e-specific gene cassette (3,071 bp) which consists of two genes, gltA and gltB, and is flanked by palindromic sequences (51 and 44 nucleotides). Complete loss of reactivity with the three serotype-specific MAbs resulted from insertional inactivation of either gltA or gltB. The gltA and gltB mutants were characterized by loss and severe reduction, respectively, of glucose in the teichoic acid, whereas galactose, the other serotype-specific sugar substituent in the teichoic acid, was not affected. Within L. monocytogenes, only strains of serotypes 4b, 4d, and 4e harbored the gltA-gltB cassette, whereas coding sequences on either side of the cassette were conserved among all serotypes. Comparative genomic analysis of a serotype 1/2b strain showed that the 3,071-bp gltA-gltB cassette was replaced by a much shorter (528-bp) and unrelated region, flanked by inverted repeats similar to their counterparts in serotype 4b. These findings indicate that in the evolution of different serotypes of L. monocytogenes, this site in the genome has become occupied by serotypespecific sequences which, in the case of serotype 4b, are essential for expression of serotype-specific surface antigens and presence of glucose substituents in the teichoic acids in the cell wall.

Microbiological Aspects of the Investigation That Traced the 1998 Outbreak of Listeriosis in the United States to Contaminated Hot Dogs and Establishment of Molecular Subtyping-Based Surveillance for Listeria monocytogenes in the PulseNet Network

“…However, in this 1998 to 1999 multistate outbreak traced to contaminated hot dogs, a different strain type of serotype 4b, with a genetic fingerprint rarely encountered before, was identified and designated ECII. As previously reported by Evans et al (11), the ECII strains were markedly divergent in (or completely lacked) specific open reading frames that were probably involved in the expression of a cell surface component (16,23).…”

Listeria monocytogenes Serotype Identification by PCR

“…ther subtyped by using GLT primers designed from a 1/2b serotype-specific region flanking the gltA-gltB cassette (Table 1) (18). All 4b strains were negative (n ϭ 35), and all 1/2b strains were positive (n ϭ 20) when tested with these primers (Table 2, Fig.…”

“…Therefore, we hypothesized that serotyping PCR primers may be designed as an alternative to the slide agglutination method of serotyping. Primers were designed by using genomic regions that had been previously identified as diverse by sequence analysis, monoclonal antibody binding, and/or microarray analysis (4,8,18,25). In particular, microarray subtyping has been previously used to identify regions of the genome that vary between phylogenetic division and/or serotype (4,8).…”

Listeria monocytogenesSurface Proteins: from Genome Predictions to Function

“…Interestingly, serotype 4b strains are unique in bearing both galactose and glucose substituents on the GlcNAc of TA. This particularity is related to the presence in these strains of specific genes, such as gtcA, gltA, and gltB (106,144).…”