Commensal bacteria influence Escherichia coli O157:H7 persistence and Shiga toxin production in the mouse intestine.

The presence of commensal flora reduced colonization of Escherichia coli O157:H7 and production of Shiga toxin (Stx) in the murine intestine. Stx production was not detected in mice colonized with E. coli that were resistant to the Shiga toxin phage, but it was detected in mice colonized with phage-susceptible E. coli.

Diversity and host range of Shiga toxin-encoding phage.

Shiga toxin 2 (Stx2) from the foodborne pathogen Escherichia coli O157:H7 is encoded on a temperate bacteriophage. Toxin-encoding phages from C600::933W and from six clinical E. coli O157:H7 isolates were characterized for PCR polymorphisms, phage morphology, toxin production, and lytic and lysogenic infection profiles on O157 and non-O157 serotype E. coli. The phages were found to be highly variable, and even phages isolated from strains with identical pulsed-field gel electrophoresis profiles differed. Examination of cross-plaquing and lysogeny profiles further substantiated that each phage is distinct; reciprocal patterns of susceptibility and resistance were not observed and it was not possible to define immunity groups. The interaction between Shiga toxin-encoding phage and intestinal E. coli was examined. Lytic infection was assessed by examining Shiga toxin production following overnight incubation with phage. While not common, lytic infection was observed, with a more-than-1,000-fold increase in Stx2 seen in one case, demonstrating that commensal E. coli cells can amplify Shiga toxin if they are susceptible to infection by the Shiga toxin-encoding phages. Antibiotic-resistant derivatives of the Stx2-encoding phages were used to examine lysogeny. Different phages were found to lysogenize different strains of intestinal E. coli. Lysogeny was found to occur more commonly than lytic infection. The presence of a diverse population of Shiga toxin-encoding phages may increase the pathogenic fitness of E. coli O157:H7.

Acellular pertussis vaccines and complement killing of Bordetella pertussis.

Antibody-dependent complement killing of Bordetella pertussis after immunization with a three-component acellular pertussis vaccine was characterized. Postimmunization activity was unchanged for about half of the adult vaccine recipients. The responses of the other individuals were complex, with evidence of both beneficial and antagonistic responses occurring, sometimes in the same individual.

Reduced glutathione is required for pertussis toxin secretion by Bordetella pertussis.

The abilities of cysteine-containing compounds to support growth of Bordetella pertussis and influence pertussis toxin transcription, assembly, and secretion were examined. Cysteine is an essential amino acid for B. pertussis and must be present for protein synthesis and bacterial growth. However, cysteine can be metabolized to sulfate, and high concentrations of sulfate can selectively inhibit transcription of the virulence factors, including pertussis toxin, via the BvgAS two-component regulatory system in a process called modulation. In addition, pertussis toxin possesses several disulfide bonds, and the cysteine-containing compound glutathione can influence oxidation-reduction reactions and perhaps disulfide bond formation. Bacterial growth was not observed in the absence of a source of cysteine. Oxidized glutathione, as a sole source of cysteine, also did not support bacterial growth. Cysteine, cystine, and reduced glutathione did support bacterial growth, and none of these compounds caused modulation at the concentrations tested. Similar amounts of periplasmic pertussis toxin were detected regardless of the source of cysteine; however, in the absence of reduced glutathione, pertussis toxin was not efficiently secreted. Addition of the reducing agent dithiothreitol was unable to compensate for the lack of reduced glutathione and did not promote secretion of pertussis toxin. These results suggest that reduced glutathione does not affect the accumulation of assembled active pertussis toxin in the periplasm but plays a role in efficient pertussis toxin secretion by the bacterium.