Campylobacter jejuni chromosomal sequences that hybridize to Vibrio cholerae and Escherichia coli LT enterotoxin genes

AB(5) toxins: structures and inhibitor design

High-resolution crystal structures of AB(5) toxins in their native form or in complex with a variety of ligands have led to the structure-based design and discovery of inhibitors targeting different areas of the toxins. The most significant progress is the development of highly potent multivalent ligands that block binding of the toxins to their receptors.

Campylobacter upsaliensis: waiting in the wings

Despite strong epidemiological evidence supporting an important role for Campylobacter upsaliensis as a human enteropathogen, it remains relatively unknown in the realm of clinical microbiology. Clinical studies indicate that infection with this organism usually is associated with benign self-limiting diarrhea. However, more serious illnesses, including spontaneous abortion and hemolytic-uremic syndrome, recently have been associated with human infections. Understanding of the virulence properties and molecular biology of C. upsaliensis is beginning to evolve. There is now a pressing need for controlled, prospective epidemiologic studies in addition to further in-depth investigation of the pathogenesis of this enteric campylobacter to more precisely define its role in human disease. Furthermore, since C. upsaliensis is sensitive to the antibiotics routinely used in Campylobacter selective media, widespread appreciation of the importance of this organism will rely on the development of widely applicable, effective techniques for its isolation.

Toxin production by Campylobacter spp

Of all the virulence factors that were proposed for Campylobacter jejuni and related species to cause disease in humans, the discovery of toxin production was the most promising but led to a rather confusing and even disappointing stream of data. The discussion of whether proteinaceous exotoxins are relevant in disease remains open. One important reason for this lack of consensus is the anecdotal nature of the literature reports. To provide a basis for an unbiased opinion, this review compiles all described exotoxins, compares their reported properties, and provides a summary of animal model studies and clinical data. The toxins are divided into enterotoxins and cytotoxins and are sorted according to their biochemical properties. Since many Campylobacter toxins have been compared with toxins of other species, some key examples of the latter are also discussed. Future directions of toxin research that appear promising are defined.

AB5 toxins

Crystal structures of shiga and pertussis toxins have recently revealed a remarkable degree of structural homology among the members of the AB5 class of bacterial toxins. Other structures have provided a detailed view of the molecular basis of receptor binding specificity of cholera toxin, and of the heat-labile enterotoxin of Escherichia coli. These structures also provide tantalizing, but as yet incomplete, information on the site of ADP-ribosylation in the homologous A-subunits of the Escherichia coli heat-labile toxin, cholera toxin, and pertussis toxin.

Immunological properties and ganglioside recognitions by Campylobacter jejuni-enterotoxin and cholera toxin

The immunological properties of Campylobacter jejuni enterotoxin (CJT) and cholera toxin (CT) were compared by enzyme-linked immunosorbent assay (ELISA) and Western blotting analysis with antiserum against each toxin. Antibody against CJT recognized the 68, 54 and 43 kDa polypeptides of CJT and the 11 kDa subunit of CT, whereas antibody against CT recognized the 68 and 54 kDa polypeptides of CJT and 11 kDa subunit of CT. The immunological reactions between the heterogeneous combinations of toxins and the antibodies were weaker than those between the homogenous systems. Thus, different antigenicity was found in CJT and CT at the subunit level, although they possessed cross-reactive epitope(s). The binding of CJT and CT to gangliosides was also examined. CJT and CT bound to GM1 ganglioside preferentially than to other ganglioside species. However, CJT did not bind to GD1b in spite of the fact that CT preferred GD1b. This suggests that both toxins recognize different receptors on the surface of the target cell. This study is the first demonstration of the different properties between CJT and CT in immunological character and ganglioside recognition.

Altered synthetic response of Campylobacter jejuni to cocultivation with human epithelial cells is associated with enhanced internalization

Campylobacter jejuni has been shown to bind to and enter epithelial cells in culture. The interaction of C. jejuni with INT 407 epithelial cells was examined to determine whether bacterial protein synthesis is required for either binding or internalization. Chloramphenicol, a selective inhibitor of bacterial protein synthesis, significantly reduced the internalization, but not binding, of C. jejuni compared with untreated controls as determined by protection from gentamicin. Electrophoretic analysis of metabolically labeled proteins revealed that C. jejuni cultured with INT 407 cells synthesized 14 proteins that were not detected in organisms cultured in medium alone. The inhibitory effect of chloramphenicol on internalization was reduced by preincubation of C. jejuni with INT 407 cells. The results indicate that C. jejuni, like some other enteric pathogens, engages in a directed response to cocultivation with epithelial cells by synthesizing one or more proteins that facilitate internalization and suggest that this phenomenon is relevant to the pathogenesis of enteritis caused by C. jejuni.

Molecular genetic analysis of ganglioside GD1b-binding activity of Escherichia coli type IIa heat-labile enterotoxin by use of random and site-directed mutagenesis

Mutagenesis of the B-subunit gene of Escherichia coli heat-labile enterotoxin LT-IIa was performed in vitro with sodium bisulfite. Mutants were screened initially by radial passive immune hemolysis assays for loss of binding to erythrocytes. Mutant B polypeptides were characterized for immunoreactivity; for binding to gangliosides GD1b, GD1a, and GM1; for formation of holotoxin; and for biological activity. Mutant alleles that determined altered binding specificities were sequenced. Three such mutant alleles encoded Thr-to-Ile substitutions at residues 13, 14, and 34 in the mature B polypeptide of LT-IIa. Each mutant protein failed to bind to ganglioside GD1b, although the Ile-14 mutant retained the ability to bind to ganglioside GM1. Site-specific mutagenesis was used to construct mutants with various amino acid substitutions at residue 13, 14, or 34. Only those mutant proteins with Ser substituted for Thr at position 13, 14, or 34 retained the ability to bind to ganglioside GD1b, thereby suggesting a role for the hydroxyl group of Thr or Ser in ganglioside GD1b binding.