Independent and coordinate effects of ADP-ribosyltransferase and GTPase-activating activities of exoenzyme S on HT-29 epithelial cell function.

Type III-mediated translocation of exoenzyme S (ExoS) into HT-29 epithelial cells by Pseudomonas aeruginosa causes complex alterations in cell function, including inhibition of DNA synthesis, altered cytoskeletal structure, loss of readherence, microvillus effacement, and interruption of signal transduction. ExoS is a bifunctional protein having both GTPase-activating (GAP) and ADP-ribosyltransferase (ADPRT) functional domains. Comparisons of alterations in HT-29 cell function caused by P. aeruginosa strains that translocate ExoS having GAP or ADPRT mutations allowed the independent and coordinate functions of the two activities to be assessed. An E381A ADPRT mutation revealed that ExoS ADPRT activity was required for effects of ExoS on DNA synthesis and long-term cell rounding. Conversely, the R146A GAP mutation appeared to have little impact on the cellular effects of ExoS. While transient cell rounding was detected following exposure to the E381A mutant, this rounding was eliminated by an E379A-E381A ADPRT double mutation, implying that residual ADPRT activity, rather than GAP activity, was effecting transient cell rounding by the E381A mutant. To explore this possibility, E381A and R146A-E381A mutants were examined for their ability to ADP-ribosylate Ras in vitro or in vivo. While no ADP-ribosylation of Ras was detected by either mutant in vitro, both mutants were able to modify Ras when translocated by the bacteria, with the R146A-E381A mutant causing more efficient modification than the E381A mutant, in association with increased inhibition of DNA synthesis. Comparisons of Ras ADP-ribosylation by wild-type and E381A mutant ExoS by two-dimensional electrophoresis found the former to ADP-ribosylate Ras at two sites, while the latter modified Ras only once. These studies draw attention to the key role of ExoS ADPRT activity in causing the effects of bacterially translocated ExoS on DNA synthesis and cell rounding. In addition, the studies provide insight into the enhancement of ExoS ADPRT activity within the eukaryotic cell microenvironment and into possible modulatory roles that the GAP and ADPRT domains might have on the function of each other.

Nosocomial outbreak of Campylobacter jejuni meningitis in newborn infants.

In a nosocomial outbreak of Campylobacter jejuni infection 11 newborn infants (7 female, 4 male) had meningitis. The outbreak was caused by a single strain of C jejuni, as demonstrated by biotyping (biotype I), serotyping (LAU 7/PEN 18 on heat-stable antigens, a new serotype on heat-labile antigens), and the identical susceptibility pattern and outer-membrane-protein profile on sodium dodecyl sulphate/polyacrylamide gel electrophoresis. Specific antibodies against the outbreak strain (enzyme-linked immunosorbent assay and Western blot) developed in all the babies. They were treated with gentamicin and ampicillin. All but one baby, who had a moderately dilated left lateral ventricle after the meningitis, recovered well. The source of infection could not be clearly determined. Thus, C jejuni can cause serious nosocomial infection; it should be considered as a possible agent of meningitis of unknown origin, particularly in newborn infants and other compromised hosts.